# Digifant Idle Problems (revised)



## Coupe_88 (Feb 7, 2003)

This Is a write-up that will hopefully help Digi-Fart around the world
for 8valve Golfs and Jettas built from 1988 - 1992
Here was my problem:
My car's Idle would bounce anywhere from 400-1200 rpm. The car would eventually stall if I didnt babysit it.
My car would also Buck when I let off the gas and when i would coast.
A quick checklist of things i had checked while attempting to fix my bad idle/bucking
-a clean isv
-a good o2 sensor
-a good coolant temp sensor (CTS)
-no vaccum leaks
-good intake boot
-good fuel pumps
-good MAF sensor. 
-good Idle screw O-ring
-proer ignition and cam timing. 
-good ground wires to the ECU

The cure? - 
There is a switch on the bottom of the throttle body , It looks exactly like the Full Throttle switch, but on the bottom side of the Throttle body
This switch is the Idle Switch, it gets pressed in at closed throttle and switches the ECU into its Idle circuit, (minimizes fuel flow etc.)
As time passes this switch gets moved a little and the linkage cant switch it on anymore so it now has to be adjusted 
How do you know if this problem applies to you? a quick guess is to see if your car stalls when you unplug the CTS :
The more certain way to check this is :
1- by listening for the switch to click ( same noise that the full throttle switch makes except you should hear it click as soon as you open the throttle with your hand instead of WOT. ) the engine should be off for you to be able to hear it .
2- by unplugging the 2 wire harness on the throttle body , ignition on, hook up a continuity tester to the 2 prongs and there should
be continuity at closed throttle, 
if its not clicking or theres no continuity:
there are 2 tiny TORX head T-20 screws that you need to loosen so you can adjust the switch to the point where it will be actuated when you let off the throttle..... 









Good luck! 



[Modified by Coupe_88, 10:32 PM 2-28-2003]


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## MidnightGLI (Dec 15, 2001)

*Re: Digifant Idle Problems (Coupe_88)*

nice write up...
i'll add my problem/solution to this post.
my problem goes along with the vaccum leaks, check all your vaccum hoses and replace them all, they are cheap. but when checking for vaccum leaks, don't forget to check the seal at the PCV valve and the valve cover. make sure it's tight and sealed, my grommet was cracked in half and was causing all kinds of havoc with my idle when cold. also check the oil filler cap. i know these are stupid problems, but often and easily over looked.
http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif


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## Cab42 (Aug 23, 2004)

*Re: Digifant Idle Problems (Coupe_88)*


_Quote, originally posted by *Coupe_88* »_How do you know if this problem applies to you? a quick guess is to see if your car stalls when you unplug the CTS

What is the expected behavior of the idle if CTS is disconnected?


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## adub96 (Nov 12, 2003)

*Re: Digifant Idle Problems (Cab42)*

Lets not forget timing and correct timing procedure with the digifants everybody. If your timing and idle and everything is set correctly your motor should idle at or around 1100 with the blue sensor unplugged. Thats if your timing, VAF, and idle screw are all adjusted properly. After you check all the other problems up there make sure to time your car right. Get the timing adjusted properly, connected the sensor rev it three times over a 3000 let it sit and check the timing again. I usually do it twice just to make sure. Besides all that digi's just seem to have bad idle tendencies. A digi that idles perfectly should be put into the Smithsonian because it would be truly a feat of science.


_Modified by adub96 at 12:54 PM 2-17-2005_


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## Black_cabbie (Jul 16, 2003)

*Re: Digifant Idle Problems (Cab42)*


_Quote, originally posted by *Cab42* »_
What is the expected behavior of the idle if CTS is disconnected?

Depends if the car is cold or hot. If it still cold and you unplug it will probably die. Slowly with a lot of sputtering and coughing. 
If its hot and you unplug it the idle will change a bit. I think it goes a bit higher than normal.


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## Mortal_Wombat (Jan 29, 2004)

another way to cure a the same problem with a different cause is to set the idle with both the blue cts and the ISV disconnected
if the car can idle wiht out both of those it sure as hell can idle dead on with the isv connected (its how my car is setup and it idles like a freakin dream)


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## joelmahoney (Feb 20, 2002)

*Re: (Mortal_Wombat)*

I was surprised to learn that even w/o an IAC, my car idles beautifully when the idle switched is (manually activated). prepping the car, originally CIS now digi II, for MSnS... *can anyone tell me how the digi system controls the idle speed?? * is it timing? fuel? or both? 
edit: I know the timing is varied to maintain idle... I guess I'm just wondering if the fuel is also used to control it.
Thanks!


_Modified by joelmahoney at 2:04 AM 2-19-2005_


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## quadmodrophenia (Dec 6, 2002)

*Re: (joelmahoney)*

Anyone want to tell me where I can get the o-ring for the idle screw on the TB? I can't match one up anywhere that fits proper like.
So many problems taken care of when I yanked the ISV and re-routed it. Now all I have to do is get that damn o-ring so my idle doesn't change itself after some "spirited" driving.


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## VDub2625 (Jan 4, 2003)

*Re: (quadmodrophenia)*

Just go "borrow" a whole screw from the junkyard


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## quadmodrophenia (Dec 6, 2002)

*Re: (VDub2625)*

Funny, that's exactly what my parts guy said at the dealer


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## Bad Rabbit Habit (May 5, 2005)

*Re: (quadmodrophenia)*

Would this work for CIS-E engines also? I have a 86 golf, with the same symptoms.


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## braol (Jun 26, 2005)

*Re: Digifant Idle Problems (Coupe_88)*

While all these things sound great, the Idle Control Valve is usually not the problem. What is almost always bad is the throttle plates (or butterfly valves) inside the throttle body. Over time they get gummed up, especially inside the pivot pin area (the place where the valves fit inside the throttle body). The secondary valve (the small one) gets stuck slightly ajar and gives the car 'false air,' leaning out the mixture, and making the car hunt for a good idle. The easy solution is to buy a new throttle body....but since that is very expensive, the next thing is to do a "rebuild" of the throttle body. It's just really a disassembly, cleaning, and reassembly. Take some digital pictures or make some drawings as you go. It's not too hard. There is a spring or two that can be tricky to put back on the throttlebody, but they are big and not easy to break or lose.


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## Black_cabbie (Jul 16, 2003)

*Re: Digifant Idle Problems (braol)*

I did the TB "rebuilt" too, and I saw a difference in throttle response and a better smoother idle.


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## MK2SnowPilot (Sep 8, 2005)

*Re: Digifant Idle Problems (Coupe_88)*


_Quote, originally posted by *Coupe_88* »_This Is a write-up that will hopefully help Digi-Fart around the world
for 8valve Golfs and Jettas built from 1988 - 1992
Here was my problem:
My car's Idle would bounce anywhere from 400-1200 rpm. The car would eventually stall if I didnt babysit it.
My car would also Buck when I let off the gas and when i would coast.
A quick checklist of things i had checked while attempting to fix my bad idle/bucking
-a clean isv
-a good o2 sensor
-a good coolant temp sensor (CTS)
-no vaccum leaks
-good intake boot
-good fuel pumps
-good MAF sensor. 
-good Idle screw O-ring
-proer ignition and cam timing. 
-good ground wires to the ECU

The cure? - 
There is a switch on the bottom of the throttle body , It looks exactly like the Full Throttle switch, but on the bottom side of the Throttle body
This switch is the Idle Switch, it gets pressed in at closed throttle and switches the ECU into its Idle circuit, (minimizes fuel flow etc.)
As time passes this switch gets moved a little and the linkage cant switch it on anymore so it now has to be adjusted 
How do you know if this problem applies to you? a quick guess is to see if your car stalls when you unplug the CTS :
The more certain way to check this is :
1- by listening for the switch to click ( same noise that the full throttle switch makes except you should hear it click as soon as you open the throttle with your hand instead of WOT. ) the engine should be off for you to be able to hear it .
2- by unplugging the 2 wire harness on the throttle body , ignition on, hook up a continuity tester to the 2 prongs and there should
be continuity at closed throttle, 
if its not clicking or theres no continuity:
there are 2 tiny TORX head T-20 screws that you need to loosen so you can adjust the switch to the point where it will be actuated when you let off the throttle..... 
Good luck!

Another good and VERY quick way to test it to unplug the wires and connect a test wire between the two - simulating the "Idle" condition for the ECU. If This makes a difference it's most likely your problem!

http://****************.com/smile/emthup.gif







http://****************.com/smile/emthup.gif


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## taskahead (May 16, 2006)

*Re: Digifant Idle Problems (LewsCabbyTherin)*

Hi and thanks for this information. I have been searching for answers and this is the first specific info about an idle switch issue that I have found. I will try it. I have another question. Does a malfunctioning idle switch cause sluggish acceleration? The problem my 90 8V(RV) is having is sluggish acceleration and when it does this it almost always idles rough(lots of vibration) and some times will hang high around 1300rpm then come down. seems to be affected by air and engine temperature. Worse when warm. I have replaces temp sensor, O2, checked and cleaned Idle Stabilizer and put in new plugs. Occasionaly it will run perfect for about 15 minutes when cool then back to sluggish and rough. Any thoughts? What about MAF?


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## nofx1981 (Oct 24, 2006)

*Re: Digifant Idle Problems (taskahead)*


_Quote, originally posted by *taskahead* »_Hi and thanks for this information. I have been searching for answers and this is the first specific info about an idle switch issue that I have found. I will try it. I have another question. Does a malfunctioning idle switch cause sluggish acceleration? The problem my 90 8V(RV) is having is sluggish acceleration and when it does this it almost always idles rough(lots of vibration) and some times will hang high around 1300rpm then come down. seems to be affected by air and engine temperature. Worse when warm. I have replaces temp sensor, O2, checked and cleaned Idle Stabilizer and put in new plugs. Occasionaly it will run perfect for about 15 minutes when cool then back to sluggish and rough. Any thoughts? What about MAF?
 
That sounds exactly like the problems i'm having, havnen't been able to find the problem, it's really f'n anoying, plz lemme know if you find the problem


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## Coupe__88 (Sep 14, 2003)

*Re: Digifant Idle Problems (nofx1981)*

holy shipballs batman! I havent viewed this forum for 2-3 years ( i posted this topic 3 years ago ) and I just came to pop in and what do I find, one of my posts lingering on the list of topics hah!








Taskahead: No, the idle switch circuit is open off idle and has no effect on performance, it simply just tells the ECU " Hey! digifook!, do your idle thing!" This car does not have a TPS ( throttle position sensor) which tells the ECU things at any/every point of throttle travel which makes it easy to diagnose things on our cars , its just a WOT and an idle switch. As for your poor running while the car is warm you are experiencing some bad inputs from your sensors ( CTS, O2, possibly Vane Air Meter (what you called a MAF)) meaning that your car is going to run pretty smooth while it is still in open loop mode but when the engine and 02 sensor warm up and it switches to closed loop, then the computer actually clocks in for the day and goes to work thinking its doing a good job but it cant because its tools ( the sensors ) are telling it lies, Its the same kinda thing like when you tell your mom or your wife that you are out of toilet paper when you actually have 5 rolls and then she goes and gets a whole bunch more toilet paper and then you end up with more than you need and with an engine, that equates to crap. 
-_-_-_-ASSUMING that your 02 sensor was wired in properly ( soldered well, clean connection) that there are no air leaks before the o2 sensor ( ex. manifold leak) 
and that you put good spark plugs that have been gapped correctly and base ignition timing is set properly to 6 degrees advance and that your coolant temperature sensor is good along with the wiring for it. I can recommend a couple things. 
1-Seafoam
2-Clean , repair, replace groundwires. Make new ones if necessary. I like to put a new one from the negative terminal to the tranny , then to the top of the valve cover, and then from the ecu case to the chassis. this will clean up the performance/response considerably if your grounds are like most 20 year old VW grounds. 
3-Might as well try a different Airflow meter, borrow one from a friend while he isnt looking and see if it reacts differently. 
Let us know what happens -Coupe


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## 66Cooper (Oct 29, 2004)

*Re: Digifant Idle Problems (Coupe_88)*

Wow, all I can say is THANKS!!! Finally had it with my Golf reving as it feels fit, anywhere from 800 up to 2500 then down to almost stalling. Even in traffic if you just started to go and put the clutch in, it would rev up to almost 3K. Well, i took all your advice and went at it tonight. I took the throttle body off and completely cleaned it out, Regapped and cleaned the plugs (till I get newe ones) Cleaned the ISV AND fixed my idle switch which wasnt being pushed. 
I took it out for a spin and its like a new car! It stayed at 800 whenever not driving. No dips, bounces, rev-up, NOTHING!
Thanks again for everyones great advise on here. I'm actually looking forward to my comute tomorrow. You guys rules.


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## Washburn (Jan 31, 2007)

*Re: Digifant Idle Problems (66Cooper)*

Does anyone have a part number for the Idle Switch? Having a hard time locating something. I have a number here, but I'm not sure if it's correct: 037-133-093D
My dealer says this switch is bad. (Doesn't make sense since the car shows these symptoms only part of the time.) Any help is greatly appreciated.
BTW...this is a great forum...glad I found it!!


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## Gede Nimbo (Aug 13, 2004)

*Re: Digifant Idle Problems (Coupe_88)*

My 91' Digi 2 Golf 8V has a problem with cold idle when started up. It will not idle above 400 rpm and runs rich until it warms up a bit then idles at 900rpm which I set it to. I'm at my wit's end with this engine and will go onto 16V Digi 2 soon but I wanted to drive the car on the 8V first. Where do I start my investigations,
replaced HG, intake, exhast gaskets, ported Digi 2 head
I checked all the electrical connections/plugs and cleans
Cleaned ISV, 
Cleaned MAF
replaced the black coolant temp sensor
flushed coolant and radiator
Installed Low temp fan switch and T stat (Car runs a bit hot before the fan cycles)
New head gasket


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## Elamb123 (Sep 28, 2007)

do you have to take the TB off too adjust the idle switch on the bottom? I cant seem to get a screwdriver or anything else on there with it on!!!


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## XLJesse (Jul 28, 2007)

*Re: Digifant Idle Problems (Coupe_88)*

my car recently has been being a bitch.... i recently put in a new ISV because my old one was busted, since i put in my new one its been doing some real funny things i dont know if it has anything to do with the ISV even its been raining recently aswell
Its been idling better, but now at some red lights it just bouncing from literally 200 rpm where the battery light flickers on because it almost shuts off and then it jumps up to about 1500 and then bounces up and down then shuts off. I have checked all my sparks plugs and wires.. i also i have sprayed around the valve cover with carb medic checking if it was leaking in the seal and nothing. Vacuum hoses and everything seems to be all intact good no vacuum leaks i think its a fuel problem but i dont know what... also i will be driving and accelerating quite fast, and all of sudden it will just decelerate it will have no pull whatsoever but still reving at a high rpm just not giving any power

i know this is probably seems like alot but any info or anything would be great. if you i can give more info let me know ill do my best.


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## dirtyp (Oct 4, 2007)

check the idle switch under the t-body. i didnt even have to loosen the screws to change your symptoms on my car. just reach under there and push the switch towrds the stop.
i did it to my car which was doing the same things. you pull up to a light and let go of the gas and the revs fall down to almost stall. then it hunts to keep running. i have also had issues while driving on the hiway like what you mentioned about loosing pwr. try that switch adjustment......hey its free


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## XLJesse (Jul 28, 2007)

no doubt thanks man!


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## Chapel (Jun 23, 1999)

*Re: Digifant Idle Problems (Coupe_88)*


_Quote, originally posted by *Coupe_88* »_Here was my problem:
My car would also Buck when I let off the gas and when i would coast.

mine seems to be bucking/losing power at really low throttle inputs under load.
Seems fine if you goose it... but part throttle is weird.
I'm sure my ISV is bad... I'd been having issues with it starting and keeping started when it's cold. Under normal circumstances, when you let off the gas it would dip well below normal idle speeds and bounce. It would also buck hard at lower RPMs.


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## Gede Nimbo (Aug 13, 2004)

*Re: Digifant Idle Problems (Chapel)*


_Quote, originally posted by *Chapel* »_
mine seems to be bucking/losing power at really low throttle inputs under load.
Seems fine if you goose it... but part throttle is weird.
I'm sure my ISV is bad... I'd been having issues with it starting and keeping started when it's cold. Under normal circumstances, when you let off the gas it would dip well below normal idle speeds and bounce. It would also buck hard at lower RPMs.


Chapel,
It could be either one of 2 things or actually both at the same time. One it could be the resistor in the MAF not making correct arc-ing contact. The only way to check is to pop off the black sealed cap ontop of the MAF. There is an electrical resistor arm that makes contact and gives the values electronically to the ECU. If the grid is extremely scored or worn, you will have to replace the MAF. That is what usually causes the bucking of startup atleast on mine. I replaced my MAF with a new unit. Secondly, It could also be the ECU which is actually a common site. Sometimes the ECU shorts internally due to a weird grounding situation. I had one ECU fry in a customer's car just trying to start it up. 
As you know, Be aware that the Digifant cars are extremely dependent on a strong clean spark, Check the Cap and wires, Plus foul but not unless regularly maintained. http://****************.com/smile/emthup.gif


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## Chapel (Jun 23, 1999)

*Re: Digifant Idle Problems (Gede Nimbo)*

I recently installed the DigiFast2 chip from VW_pilot as well.
I'll check the MAF and the spark plugs (which have about 20k miles on them)
It might just be a plug change.
cap and wires were done around 20k miles ago as well.


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## goosler (Feb 11, 2002)

*Re: Digifant Idle Problems (Coupe_88)*

bump


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## snowdub20 (Oct 28, 2007)

all this talk about throttle bodies....would a larger one give more power, since more air would be going in and the throttle would have a bigger opening. if so, where could i find one? any possibilities?


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## sholford (May 21, 2007)

*Re: (snowdub20)*


_Quote, originally posted by *snowdub20* »_all this talk about throttle bodies....would a larger one give more power, since more air would be going in and the throttle would have a bigger opening. if so, where could i find one? any possibilities?


I'd look at it like this...I'm sure someone will chime in if I'm wrong.
If you're trying to pull more air into a stock engine, you're probably wasting your time. You need to increase the breathing capacity of the engine (bigger cam, free flowing exhaust, maybe head work) to take advantage of a bigger throttle body. This is the same mistake people make with the bigger BMW afm. Think of it like hooking a funnel up to a straw. You have a big opening but everything else is only going to flow so much until you open it up. Another thing to think about is volumetric efficiency. If you go too big with a throttle body...especially on a stock engine, you'll hurt your throttle response. Use the search function and you'll find some info. Hope this helps.
If you have a stock 8v Golf, try a dual downpipe and manifold for the exhaust. If I remember correctly, the GTI's had a slightly bigger throttle body as well. 


_Modified by sholford at 2:46 AM 7-1-2008_


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## snowdub20 (Oct 28, 2007)

*Re: (sholford)*

Alright yeah thats understandable, i see what you mean. i'll do some other things and save that for later, if i even want to do it in the end. I have other things to work on before that. 
thanks


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## Coupe__88 (Sep 14, 2003)

*Re: (snowdub20)*

Correct, the VAM and ports become bottlenecks before the TB and intake manifold do. A larger TB , like most intake mods, will really only improve response on these cars, not power.


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## IfItsNotGermanItsCrap (Jul 12, 2008)

*Re: Digifant Idle Problems (Coupe_88)*

A solution for the bucking might be to replace the front motor mount. Fortunately, this is probably the easiest of all motor mounts to replace. (If you've ever had to do the passenger side you know what I mean. It's a real PITA). You can see it underneath the radiator- and it's easy to tell if its busted. My girlfriend has an '87 Cabby and it was busted for so long it eventually caused the inboard CV joints to fail. Changing the motor mount not only dampened many of the vibrations but also made the car shift like new.


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## TwelveValve VR (Mar 25, 2006)

im also experiencing many of the symptoms everyone has posted above. i replaced plugs and wires. i will look into the cap and mess with the throttle switch and body and clean it out.
thanks for all the input !


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## JDMH22HATCH (Jul 7, 2008)

*Re: (TwelveValve VR)*

Awesome thread. Unfortunately I have all of these symptoms listed throughout the whole thread plus more







Maybe somebody can help with a few things. 
I've checked all switches, cleaned everything as mentioned above, and replaced plugs, wires, dizzy cap and rotor. My car idles ****ty off and on, bucks horribly inbetween 1300-4000 rpms whether on throttle or not, and my fan doesn't work. I jumped the fan and low speed turned on and high speed does not. I also tried to set timing, but after reaching operating temp I unplugged the CTS and the car died. Tried to start it up without it unplugged and died immediately. Any input would be great http://****************.com/smile/emthup.gif

_Modified by JDMH22HATCH at 2:38 PM 9-25-2008_


_Modified by JDMH22HATCH at 7:39 AM 9-27-2008_


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## sholford (May 21, 2007)

*Re: (JDMH22HATCH)*


_Quote, originally posted by *JDMH22HATCH* »_Awesome thread. Unfortunately I have all of these symptoms listed throughout the whole thread plus more







Maybe somebody can help with a few things. 
I've checked all switches, cleaned everything as mentioned above, and replaced plugs, wires, dizzy cap and rotor. My car idles ****ty off and on, bucks horribly inbetween 1300-4000 rpms whether on throttle or not, and my fan doesn't work. I jumped the fan and low speed turned on and high speed does not. I also tried to set timing, but after reaching operating temp I unplugged the CTS and the car died. Tried to start it up without it unplugged and died immediately. Any input would be great http://****************.com/smile/emthdown.gif 

_Modified by JDMH22HATCH at 2:38 PM 9-25-2008_

Electrical problems.....meaning grounds or broken wires are #1 digifant issues. Any wiring that is green, frayed or broken needs to be replaced. If you see a broken connector bolted somewhere, find the wire and replace it. 
-Broken throttle switch wiring is something to check
-Bad grounds especially
-O2 ground at driver's side of the engine....water outlet bolt.
I was highly pissed for a week because I couldn't figure out why the car wouldn't idle right, and it was running rich. It was the broken ground at the water outlet used for the o2 sensor.


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## datavirtue (Aug 1, 2008)

*Re: Digifant Idle Problems (Coupe_88)*

Make sure the timing is perfect before trying to hunt down other gremlins. Timing that is off 3 degrees will make a sloppy idle and bad throttle response.
Check out Techtonics Tuning website for pictures on how to set your timing easily and accuratly by eye.


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## kuleinc (May 10, 2009)

*Re: Digifant Idle Problems (datavirtue)*

So what would cause the engine to take off like you floored it when you were taking off normally from a stop?


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## helicfii (Apr 15, 2009)

*Re: Digifant Idle Problems (kuleinc)*

An Audi name badge?


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## Rabbid0281 (Jan 12, 2008)

*Re: Digifant Idle Problems (kuleinc)*


_Quote, originally posted by *kuleinc* »_So what would cause the engine to take off like you floored it when you were taking off normally from a stop?

Yeah man, mine does that. When it decides to go in that mode, its like digital throttle and i get cruise control mode on the HWY. However, Ive had the car since Feb 03, and Ive replaced a countless list of parts that were just old or degraded. Mine will be idling, regardless of outside temp, and then just all the sudden shoot up to 4200 and bounce between 2000. I killed my ignition switch thinking i could reset it, so now i have wires rigged to "hotwire" and start it. TY Bentley wiring schematics. 
Right now that is my biggest problem, and the fact the factory fan setup was tossed when it died, in favor of those flex-lite units. i can fit 2 of the 50$ kits on there, but can get it to work from the factory harness, so its wired into my aux running lights.... you would not believe how jerry rigged this car is. my pedal bracket rusted and broke from under the dash, which was sorta welded back in place by a friend, but after sitting for 2 years in the TX heat, it broke again. I miss my Jetta!


















_Modified by Rabbid0281 at 6:17 PM 8-29-2009_


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## Rabbid0281 (Jan 12, 2008)

*Re: (snowdub20)*


_Quote, originally posted by *snowdub20* »_all this talk about throttle bodies....would a larger one give more power, since more air would be going in and the throttle would have a bigger opening. if so, where could i find one? any possibilities?


From my understanding, the Digi system will compensate the AFR up to a certain point, then after that, it wont adjust the fuel amount no matter how much air flows. It was originally designed to be an economical alternative to BOSCH's setup. Aka, its a fuel miser setup. Which wouldve made sense 20 something years ago, but is just not that practical for high performance applications, like how you can tune CIS setups for that. Correct me if I'm wrong, but I'm going off information have accumulated throughout the years of owning my 88 Jetta RV http://****************.com/smile/emthup.gif


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## Rabbid0281 (Jan 12, 2008)

bump


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## MannyC (May 21, 2009)

My car was doing this exact thing, idles started acting crazy at stop lights. I bought some vacuum lines and redid most of them, changed cap/rotor/plugs, cleaned out the isv, changed the fuel filter, added lucas injector cleaner. Good news is that my idle is fixed, no more revving at stop lights.
Bad news is I'm getting hesitation every now and then just cruising around town, and when I'm on the freeway and I get on the throttle it starts bucking pretty bad till I let off the throttle.
I'm glad I peeped this thread as I do have some other things to go over listed here....I love driving my Mkll and seriously would rather drive it then my MkV


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## MannyC (May 21, 2009)

So i tried a few things today, I started cleaning all electrical contacts in all the connectors and replacing them, undid the battery contacts and cleaned them. unscrewed the grounds I could get to and cleaned the surfaces and re tightened them, opened up the maf and cleaned in there as well...frigging car runs smooth as hell now...idles better then it ever did. Drove her around and waited for any bucking or idle creep...none.
I'm stoked...










_Modified by MannyC at 8:42 AM 9-5-2009_


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## kuleinc (May 10, 2009)

*Re: (MannyC)*

My problem was one of the two vacum lines coming off the throttle body, the tiny ones, I replaced those and the bucking and stuff stopped. Now I need to figure out why it pings like mad when accelerating after it gets warmed up! any ideas? Sometimes you can hear the fuel pump humming, could that be why? Not enough fuel? I can't figure out how to set the timing on it to save my life, when I unplug the stuff and rev it and set the timing to the mark on flywheel, its rediculously retarded to the point of almost not being able to get it back in the driveway, so I put the timing back to where it was when I got it for now...


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## Rabbid0281 (Jan 12, 2008)

*Re: (kuleinc)*

i would suggest that knock sensor space from TT i think it is...


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## CajunSpike (Mar 11, 2009)

*Re: (kuleinc)*

I had bad pinging on my 92 after i revived it from the graveyard. my intank pump was whining loudly too. replaced the inline pump..no difference. replaced the intank pump..car runs like it has a new engine in it. no more engine pinging. change that intank pump if its bad. also, the rubber hose from the intank pump to the fuel float assembly rots due to age. this happened on both my 91 and 92 cars. replace the rubber line between the pump and top of floatl assembly. 
My 92 car used to idle perfectly until I had to change the 02 sensor..now it pretty much stays locked to 1500 rpm at idle. Smooth but cant bring it down. 
My 91 car does that 'idle so low the engine almost dies' when you first start it, then settles in about 900 rpm, but has terrible throttle response. The more gas you give it the more it bogs down. if you lightly accelerate, it works more or less ok, but the engine has no guts like the 92 has. the 92 feels like a race car when you give it gas. 



_Modified by CajunSpike at 11:49 AM 9-28-2009_


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## Das Kraut (Nov 7, 2008)

*Re: (CajunSpike)*


_Quote, originally posted by *CajunSpike* »_I had bad pinging on my 92 after i revived it from the graveyard. my intank pump was whining loudly too. replaced the inline pump..no difference. replaced the intank pump..car runs like it has a new engine in it. no more engine pinging. change that intank pump if its bad. also, the rubber hose from the intank pump to the fuel float assembly rots due to age. this happened on both my 91 and 92 cars. replace the rubber line between the pump and top of floatl assembly. 


X2
Usually dont associate pinging with a bad fuel pump, but it makes sense. When that thing starts whining though, better act sooner than later!


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## CajunSpike (Mar 11, 2009)

*Re: (Das Kraut)*

I'm guessing the pinging may have been caused by low fuel pressure, thus less than optimal amounts of fuel injected into the cylinders resulting in ping. Now with full fuel pressure, I get no knock/ping from the engine at all.


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## IML337 (Jun 28, 2002)

*Re: Digifant Idle Problems (Coupe_88)*

I'm going to bump this because it's led me to a fix for an idle our 8v GTI has had since we bought it 18 months ago.
When I read about the throttle closed sensor switch under the throttle body moving, I knew it could be something to look at. When I checked however, I could hear it clicking as soon as the throttle was alternated between closed and open.
So I thought maybe the switch is a dud, so I grabbed a continuity tester, pulled the two prong plug off the TB, and poked around. I quickly discovered that the plug connecting to the throttle body was faulty - one of the two metal contacts inside it was pushed back into the plug and not making contact with the prongs on the TB side.
I quickly sorted it out and now
We've purchased ISV's, replaced MAF's, done the timing a million times (no pun intended) and all sorts... And it was all down to that bloody plug.
Thanks for lots of good info to those that have posted in this over the years. http://****************.com/smile/emthup.gif


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## vdubdubv (May 4, 2009)

*.:in tears:.*

I LOVE YOU GUYS!!

::cough:: ::cough::

I mean thanks for the info, as my "new" $300 91 jetta is now working at optimum performance. Might I suggest changing manual transaxle fluid to 2.1 qts of royal purple 75-90 so you can really feel those 100 horses pound the pavement (it actually gave me 2mpg!)

vdubdubv:beer:


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## rosiewoodboat (Oct 1, 2004)

*Digifant II, 8V dies when blue coolant temp sensor disconnected*

I had problems similar to those described in the original (and ancient!) post. My idle is rough when the motor is warm (although it drives just fine once the RPMs get up). I checked the idle switch and I have voltage at the harness and continuity when the idle switch is closed. Still, my car dies when the blue CTS is disconnected. That makes it hard to check/set the idle, which is supposed to be done with a warm motor and the blue CTS sensor disconnected.

Any ideas? Thanks!


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## fatmobile (Nov 11, 2002)

Mortal_Wombat said:


> another way to cure a the same problem with a different cause is to set the idle with both the blue cts and the ISV disconnected
> if the car can idle wiht out both of those it sure as hell can idle dead on with the isv connected (its how my car is setup and it idles like a freakin dream)


 I don't know much about gassers but I did work on a digi-II swap in a Rabbit and I'm pretty sure that if you disconnect the ISV with the ignition on, 
you'll ruin the ECU. 

I had to make a plug so I can check the current to the ISV, 
so it aways has power when the ignition is on. 

A bad ground, usually that one on the valve cover, will do the same thing. 

Symtoms will be weird starting out at a light.


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## zumiez82 (Aug 23, 2009)

were can i get a new idle switch i cant adjust mine far enough to make contact


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## 78CannonMK1 (Nov 4, 2010)

i have this same problem with my 78 1.6???


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## Str8pipingti (Oct 10, 2010)

adub96 said:


> Lets not forget timing and correct timing procedure with the digifants everybody. If your timing and idle and everything is set correctly your motor should idle at or around 1100 with the blue sensor unplugged. Thats if your timing, VAF, and idle screw are all adjusted properly. After you check all the other problems up there make sure to time your car right. Get the timing adjusted properly, connected the sensor rev it three times over a 3000 let it sit and check the timing again. I usually do it twice just to make sure. Besides all that digi's just seem to have bad idle tendencies. A digi that idles perfectly should be put into the Smithsonian because it would be truly a feat of science.
> 
> 
> _Modified by adub96 at 12:54 PM 2-17-2005_


 can you pm me with the proper way with the timing sequence. so is your car supposed to run like garbage when the timing is set before you plug the CTS in? i have my way advance, b/c i thought my timing light was bad. so can you just give me something other than the bentley?>


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## theshanks (Sep 14, 2011)

Im working on somones digi and the idle is giving me grief Ive never seen before. Doesnt matter hot or cold. Sometimes the idle will creep up higher, or if you take the car out of gear say at a light the idle wont drop down propery. It stays high anywear from 1100-1500. IF you kick the throttle somtimes it comes back down or if you drag the car down to a crawel in 1st or second so the rpm are bellow 1000rpm.

The ISV is clean, I cleaned it again to be sure. The CTS is fairly new too. All the switches are in working order. Id asume its not a sticky MAF sensor, that would cause it to bog out.

Could a dirty throttle body cause that? The idle was set a month ago when the car went in for fueling calibration by a pro. It worked fine for a couple weeks untill it got cold out.

Any advice appretiated!


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## theshanks (Sep 14, 2011)

quadmodrophenia said:


> Anyone want to tell me where I can get the o-ring for the idle screw on the TB? I can't match one up anywhere that fits proper like.
> So many problems taken care of when I yanked the ISV and re-routed it. Now all I have to do is get that damn o-ring so my idle doesn't change itself after some "spirited" driving.


I wonder if thats whats going on in my situation?


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## RoyC (Dec 9, 2011)

*The information in this thread is trouble-shooting GOLD!*

*Thanks to everyone who's provided troubleshooting information in this thread! :thumbup:*

My 1992 Golf 8Valve situation:

Car went from smelling a bit rich & idling at 1400 - 1500 to idling at 2700 - 3000 over the course of some months. (Bad me. I should have fixed it sooner). Fuel mileage went from great to lousy.

The fix (well, 90% of it): A new coolant temperature sensor (CTS). Cost me about $20... I bet I wasted far more than $20 worth of gas over the last few months... Sigh.

Still wasn't quit right even with the new CTS though. Further reading thru this thread (and ONLY this thread!) and I find some bad wiring connections at the plug on the throttle body where the wiring harness from the firewall plugs in.

The car now runs as smooth & nicely as it did when I bought it 7 years ago!

Next up: Preventative maint. I'll check all the troublesome electrical connections identified in this thread and make sure they're all good so I don't end up trying to fix them in the cold & dark at the side of the road somewhere. 

Edit: Dec 29: 
Found dirty, slightly corroded pins in electrical connectors around the ECM. Cleaned with a small wire brush. Sprayed on some corrosion inhibitor & reassembled. (Always disconnect battery when doing this kind of thing!!!). Car starts from cold & achieves stable idle at slightly lower rpm quicker than before. 

Found a new Bosch pn13942 O2 sensor on eBay for $35 delivered. It's for a Ford, but apparently same sensor as the VW unit (you do have to cut off the Ford plug & splice on the VW electrical plug tho.) Will install in the next couple days. The car has 267,000km on it & I'm almost certain this is the original 02 sensor, so replacement is loooong overdue.
​


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## slowride81 (Nov 21, 2011)

I'm having similar issues. When I bought the car it had some wild idle like some of the others here and also had a stalling problem. It did run rich too(at least smelled like it). I've done a LOT of work on my jetta since I bought it 3 weeks ago trying to turn it into a dependable ride. Belts, rotor, cap, plugs, wires, cts, exhaust, grounds, air filter, cleaned ISV, rewired o2 sensor (wires corroded off plug), re-soldered bad connection wires to knock sensor, cleaned corroded plug to hall sender, re-aligned and tested idle switch, ignition module, ignition coil and wiring to it, checked vacuum lines, checked computer board for any fried circuits(even tried a spare unit I got from the local pullapart), heater core and new hoses for it. I'm running out of things to do here to resolve the issue. All I think I have left to do is check the fuel regulator, replace fuel filter and check/clean the rest of the wiring (I haven't done all the wiring to the throttle body/fuel rail yet). Lastly I have not checked the timing and only done a visual inspection on the condition of the timing belt. I don't know if timing could produce this issue however.

I've come a long way from how it ran when I got it and I know i'm almost there. I'm now at the point where the car will idle perfect for a second then pulsate 100-200 rpms while sitting at a stop light or idling in the driveway. Occasionally it will kick up to 1200+ and drop almost to a stalling point but not like it used to. It does smell like its running rich though(I know smell isn't always a great indicator). I hope these last few things will fix it for good.

Edit: Failed emissions testing today. Was told be mechanic at my dads shop cat is clogged.

Edit 2: OK looks like the car is fixed. Replaced cat, made little difference. Old one was a good amount clogged however so a needed change. While trying to figure out wtf is going on I pulled the vacuum line from the fuel regulator to the air box and there it was... gas. Thankfully local parts store had one in stock. Gas + vacuum line = bad. Replaced it car runs pretty damn well now. Fires up quick first turn of the key, doesn't smell rich anymore and no stuttering.


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## 87mark2gti (May 20, 2010)

my 91 digifant2 gti has an idle problem after i rev it up idles fine until i rev it a bit rpm stays stuck between 2500 and 3500 i have to rev it again and it sometimes goes higher and stays there and drops back to around 950 then fluctuate and settles i replaced my cts and iav cleaned the throttle plates. need heeeeelp idle is irritating -_______-


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## fatmobile (Nov 11, 2002)

When I first got the DigiII Rabbit it ran rich, hunting at idle.

I disconnected the vacuum line from the fuel pressure gauge to see... 
cranked it, started it, ran better.
What's that cloud of fog coming from the engine bay? 
That's just gas fumes,.. spraying from the vacuum port on the FP regulator and hitting something hot :what:.
Diaphram broke and pressureised fuel made it to the vacuum side and was getting pumped through the vacuum line, dumping into the intake.


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## spudcar (Sep 10, 2007)

I'm having a totally new issue that I haven't seen on here yet: I've installed a newly massaged 8v head into my 90 Jetta along with intake and exhaust manifold, o2 sensor, cts etc etc. the problem is now the car only idles if I unplug the cts, if not it revs evenly for a few seconds before quickly dropping off and stalling. I'm checking grounds now and will look at the idle switch next but if that doesn't sort it I'm going to need some new ideas. 

I'm dying to drive this thing, now that it's all cleaned up it definitely seems to rev a lot more freely.


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## spudcar (Sep 10, 2007)

So the timing is good, wiring harness patched, distributer is good, injectors are clean, new plugs, new O2, CTS tests positive, and the car runs and drives pretty good (if a little lean)... But only if I keep the CTS disconnected otherwise it won't idle worth a damn. 

Should I start looking at replacing the Digi brain? Or has anyone got any new ideas I should try first?

:beer:


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## Seax_Smith (Jun 1, 2007)

Digi ECU VERY rarely fail by themselves. They usually need a little human help.

If I had you CTS issue I would:

1) replace CTS with an OEM one form the stealership, because I have had aftermarket ones test inside specs, on the edges and the car ran horrible. Had One, once, the would test dead center on the graph at room temp and at full operating temp, but was all over the place between those two temps. Opened it up and there was rust inside it.

2) Test the head grounds for resistance and continuity. Have seen and heard of those ground wires looking fine and being clean and still adding resistance to the current flow.

3) check the signal (resistance) from the O2 sensor when the car is at operating temp. 9 is rich and 2 is lean.

Almost sounds like you digi is defaulting to "limp mode", except you are saying it is leanish. In limp mode, digi is pig rich.


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## spudcar (Sep 10, 2007)

... So here's where I've got to:

-Harness is clean (at least on visual inspection, I have yet to meter every line from the ECU back)

-I just installed 
-CTS does not appear to be the issue as I tried a new VW unit and then bypassed it to run closed loop both efforts yielding the same symptoms;

Namely she cold starts extremely rich with the CTS connected and idles extremely rough until there is a little heat at which point she runs great with lots of power, steady idle etc. But as soon as she gets all the way up to operating temp it's as if something is disengaging the fuel pump, the car just sputters out. Disconnecting the CTS at this point is the only way to coax it back to life but it is very hard starting and runs very lean with the usual high idle speed.

Please tell me there is a light at the end of this nightmare!


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## Seax_Smith (Jun 1, 2007)

spudcar said:


> ... So here's where I've got to:
> 
> -Harness is clean (at least on visual inspection, I have yet to meter every line from the ECU back)
> 
> ...


There is more than light at the end of the tunnel for you. You get threw this successfully and you will never be baffled by digi again.

Part of getting my current daily up to daily reliablitiy was rebuilding pretty much all of the forward harnesses.

When you do get a meter on those wires, check for continuity AND resistance. Digi is very voltage sensitive and resistance decreasing the voltage getting to the ECU will adversely affect how the engine runs.

I got bagged on this at on point. I had continuity and practicaly 0 resistance. Eventually went old-school on the wires. Set up a test light with a 12 volt bulb (spare front marker/ directional light), with a pair of really long leads and use the brighter, directional circuit. WITH THE HARNESS OUT OF THE CAR/COMPLETELY DISCONNECTED, I ran 12 volts from the battery to one end of the wire being tested; the test light to the other end of the wire and the ground lead of the test light to the battery. Had a couple wires that would not give me full light from the bulb - broken wire inside what was good insulation. Thee was no resistance issue nor continuity issue because some of the copper strands were intact enough, but when a "load" was put on them, the results were less that stellar.

The head grounds, which are really important to digi, are a little prone to this kind of semi-failure.

Starting really rich is a sign of a bad O2 sensor.

Crapping-out at operating temp is also a sign of a bad O2 sensor.


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## turbochachi (Dec 2, 2008)

my mk2 ran like **** when i got it a few days ago the guy that had it before me didnt seem to know too much about cars i got it for 500$ traded my friend a old head unit he got me my timing belt and exhaust compoenents, but my knock sensor was the prime suspect, so i took sensor off my mk3 and she runs like a kenyan as of last night, gonna change all the grounds at some point today and clean the fueling system see how more efficiently the old girl will roll.


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