# Running rich if CTS is plugged in...



## b5in (Sep 10, 2003)

****problem solved, see my post below****



****I added a quick video below with a a/f gauge that I hooked up to see/show what's going on****

'88 golf 8v 1.8L digi2

Well I am at wits end on trying to figure out why this b!tch is running like crap so I am turning to you.

When it gets up to normal running temp. it runs rough like it's not running on all cylinders and bucks/backfires all over the place and will die if I don't stay on the throttle a little bit...

but if I unplug the CTS it runs & idles totaly fine 

I changed/checked:

-MAF
-CTS
-o2 sensor
-checked idle switch
-cleaned all grounds
-plugs
-cap & rotor
-went over intake tube & vac. lines

please help 

pics of said car


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## Eric D (Feb 16, 1999)

Green arrow is CTS, M14 thread size.
The pink arrow is also a cts but is used for your coolant temp gauge, it is an M10 thread size.

You are missing the ISV, in its place is a valve cover breather filter, and a bypassed TB to intake tube hose.

Once your add the missing parts you can then set your base idle per the Bentley.

This is a later model Digfant, but the hose set up is the same.


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## b5in (Sep 10, 2003)

ahhh yes, I deleted the isv

idle isn't the problem, even when driving it runs like poop, as long as I plug in the new CTS


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## MK2SnowPilot (Sep 8, 2005)

You must have had to adjust the idle screw in order to run without an ISV - have you checked or tried adjusting it when the car is warmed up to see if anything changes?

Were you aware that by venting the PCV to atmosphere you are creating a vacuum leak? You would have been better off plugging the hole. Oil dipsticks and the tube it goes in are vac leaks too....

Beyond that I don't see how anybody can help you. By deleting the ISV you have completely changed things. You may not consider the idle to be a problem but unfortunately the idle is the baseline for tuning an engine. By eliminating it you have hurt your ability to troubleshoot issues just to save a few bucks...


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## ziddey (Apr 16, 2006)

how have you tested the cts / o2 sensor? you say it drives fine until it warms up? sounds like o2 sensor to me. what if you leave cts plugged in, and unplug the o2 sensor? idle/wot switches working ok? knock sensor issues / improper ign timing?


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## b5in (Sep 10, 2003)

o2 sensor & CTS are brand new, I just put them in within the week.

I deleted the ISV so I don't run into a problem later on so I guess I can just re-install it but it seemed like a lot of people were running no ISV w/o problem.

When I 1st start the car it runs fine and then after approx. 10 minutes it's like someone flips a switch and if I am not on the gas it wil shut right off or stumble & die and even when I am on the gas it's bucking/missing.

same thing if I have the CTS plugged in and the o2 unplugged.

but if I unplug the CTS it's fine.


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## bretthbmx (Jun 20, 2007)

Not to hijack your thread but my digi 2 is having a problem too. Once it warms up, when on the gas it hesitates a lot and rpm dies a couple hundred then will come back. Has a new cts. Also when I unplug the cts, once I hit 3k, the motor revs a whole **** load faster.

My buddy told me it might be injectors.


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## Eric D (Feb 16, 1999)

Brett, read your Bentley manual and you'll learn how to set your base idle.
Unlike other cars, Digifant is quirky, but once you know its secrets, it isn't a big deal.


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## bretthbmx (Jun 20, 2007)

Eric D said:


> Brett, read your Bentley manual and you'll learn how to set your base idle.
> Unlike other cars, Digifant is quirky, but once you know its secrets, it isn't a big deal.


My idle and ignition timing is fine. I said nothing about the idle. It idled at 900 rpms. 

The car won't even run now. I have spark, fuel, and compression. Possible bad maf or second ecu fried? 

I don't have a bentley either. Seems like a waste of money. My mk3 one was never helpful.


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## ziddey (Apr 16, 2006)

I was able to start digi2 with no maf hooked up. It would idle fine, but of course would stall when the throttle was touched.

It is strange that you go rich if you unplug the o2 with warm cts, and yet you are fine with unplugged cts / cts not warm.

What prompted you to change the cts and o2 recently? Have you checked resistance of the cts? Is it bosch brand? I have had a cts come bad from the box. Also, was it a direct replacement o2 sensor? soldered? spliced? Have you measured o2 output on a warm engine to verify it is reporting rich?


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## b5in (Sep 10, 2003)

I got the o2 sensor changed 1st cuz it was running rich, the muffler shop put a bosch universal in so they spliced it.

Since the new o2 didn't seem to help I replaced the CTS, it was just one I ordered from Autozone.

I have a multimeter and looked up how to test the o2 & CTS but I still couldn't figure it out


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## b5in (Sep 10, 2003)

ok here's a video a took to show what's going on...

I started with the car warmed up already and the CTS unhooked otherwise it would just die anyways. Also if I hook up the CTS & unplug the o2 sensor it seems to run pretty good too, but then I don't get a a/f reading on the gauge

http://s102.photobucket.com/albums/m105/B5in/89 mk2 Golf/?action=view&current=SAM_0802.mp4


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## ziddey (Apr 16, 2006)

earlier you said that if you left the cts plugged in and unplugged the o2s, it would stall. now you say it doesn't? if so, it sounds like o2s signal is bad. how did you splice your afr sensor in? when you unplug the o2 sensor, you can plug the afr sensor directly to the o2. sounds like perhaps a bad connection.


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## b5in (Sep 10, 2003)

ziddey said:


> earlier you said that if you left the cts plugged in and unplugged the o2s, it would stall. now you say it doesn't?


The 1st time I tried it that's what it did, but I tried it again the other day and it seemed to run pretty good w/o it so I tried it a couple more times to make sure, it doesn't run as rich as it does with the CTS unplugged.

There's 3 wires to the afm gauge. 1 is a ground which I grounded to the body another for power which I ran straight to the battery + and the third I spliced into the "signal" wire of the o2 sensor.


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## Eric D (Feb 16, 1999)

bretthbmx said:


> My idle and ignition timing is fine. I said nothing about the idle. It idled at 900 rpms.
> 
> The car won't even run now. I have spark, fuel, and compression. Possible bad maf or second ecu fried?
> 
> I don't have a bentley either. Seems like a waste of money. My mk3 one was never helpful.


I feel sorry for you. The Bentley manual is only one of several manuals you'll need to understand how the Digifant system works. I don't just rely on the Bentley, but I even use the Vanagon manual as it has information not found in the Mk2 Bentley. 
It seems that starting with the Mk2, that VW changed its business model, from being reliable to being a cash cow. VW wanted people to service their own cars, but since the mid 80's VW wanted to drive away the shade tree mechanic. That is why you see less information provided in the Bentley, and VW has sole control over what it shares.

But not all is lost, you really need to help yourself before others can help you.
I find it disrespectful to ask for help if you don't want to even begin to understand how Digifant works.
If you didn't understand the Mk3 Bentley, I don't see any hope for you here. 
You should take your car to a qualified VW shop, especially one that services Vanagons, as their owners are very anal about Digifant.

I don't like to help people that have no intentions of helping themselves, I just don't like to spoon feed people. It has bitten me in the ass several times, I just go round and round regurgitating the same information and the person just doesn't get it. 
--------------------------------------------------------------------------------------------------

B5in, 
Digifant has fuel maps that rely on various engine sensors.
But the fuel maps are not always used, the ECU will use the coolant temp sensor to determine:
The amount of cold start and warm start enrichment.
Ignition timing and idle stabilization during warm-up. 
When o2 sensor, idle stabilization and full throttle switches are activated.

I highly recommend you check your ECU and various sensor terminals for corrosion or oxidation.
Use Stabilant 22A, VW published a technical service bulletin about this years ago.
I don't expect Brett to buy this expensive magic exliar from VW or on-line.
VW part # ZVW 186 001
You could buy it on-line for less if you shop around, or try a cheaper contact cleaner such as Deoxit or similar from an electronic supply store.

Also wanted to share that there is a AFM adapter cable, it was installed on my Digi1 CA Jetta, RV engine code, but not all cars got them. 

The cable looks like this, same part # for Mk2 cars.










This info is for Vanagons, but the Mk2 cars also had this issue.










Read your service manuals! :thumbup:


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## bretthbmx (Jun 20, 2007)

Eric D said:


> I feel sorry for you. The Bentley manual is only one of several manuals you'll need to understand how the Digifant system works. I don't just rely on the Bentley, but I even use the Vanagon manual as it has information not found in the Mk2 Bentley.
> It seems that starting with the Mk2, that VW changed its business model, from being reliable to being a cash cow. VW wanted people to service their own cars, but since the mid 80's VW wanted to drive away the shade tree mechanic. That is why you see less information provided in the Bentley, and VW has sole control over what it shares.
> 
> But not all is lost, you really need to help yourself before others can help you.
> ...


The mk3 bentley must be horrible compared to the mk2. Its not that i didnt understand it, the mk3 bentley really doesn't state anything but the obvious. I got my car running again. It had gas but I guess it was too low and digi is finicky to that. 

If I had the money to purchase a mk2 bentley, I would. I had one before when I had a mk2 jetta and from what I can recall, it was better then the mk3 bentley.

For some reason, my car runs smoother with the CTS unplugged, and of course idles higher. When plugged in, it seems to hesitate. It is a brand new CTS. Could it be a faulty oxygen sensor?

Also I never said anything about not wanting to learn the digi system. If you don't expect to tell people information, how do you expect them to learn?


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## Eric D (Feb 16, 1999)

bretthbmx said:


> For some reason, my car runs smoother with the CTS unplugged, and of course idles higher. When plugged in, it seems to hesitate. It is a brand new CTS. Could it be a faulty oxygen sensor?


Unplugged CTS or 02 sensor makes the car run in open loop, in other words, you are wasting fuel since the ECU is using cold start maps to override the missing sensor signals.

VW had an interval of 60K miles for the 02 sensor, how old it yours?
Not uncommon for the heater circuit to fail, or the green shielded wire to fail (VW actually sells a replacement that you wire up from the ECU plug). 
O2 sensor plugs also get water inside causing corrosion. You'll have to clean that up before replacing the sensor with a Genuine Bosch (aftermarket sensors are iffy, Bosch invented the 02 sensor for automotive apps). 

For proper idle, you must observe and follow specifically the Bentley manual for setting base idle.
There is way too much info just related to idle that I will not type, get the manual and read the fuel chapt.

It basically involves knowing that all your sensors and devices are working, it will tell you what VW tool to use for measuring mA current of the ISV and also measuring the CTS resistance to temperature in ohms. How to verify the throttle switches are working, you will also learn how to measure the resistance (ohms) of the AFM and its built-in IAT sensor measured in ohms. The AFM is typically replaced as a unit unless you have a local rebuilder that will repair yours. I repair my own AFM and most electrical and mechanical parts on my vehicles.

I strongly suggest you get the ISBN from Bentley and google it for the lowest price.


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## bretthbmx (Jun 20, 2007)

Eric D said:


> Unplugged CTS or 02 sensor makes the car run in open loop, in other words, you are wasting fuel since the ECU is using cold start maps to override the missing sensor signals.
> 
> VW had an interval of 60K miles for the 02 sensor, how old it yours?
> Not uncommon for the heater circuit to fail, or the green shielded wire to fail (VW actually sells a replacement that you wire up from the ECU plug).
> ...


Yeah I actually tested my MAF with the multi meter the other day and it was in spec. My idle is set to 900 with cts plugged in, it just automatically raises with the cts unplugged.


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## Eric D (Feb 16, 1999)

bretthbmx said:


> Yeah I actually tested my MAF with the multi meter the other day and it was in spec. My idle is set to 900 with cts plugged in, it just automatically raises with the cts unplugged.


Based on your 1st post, I would carry a multi-meter in the car, when the idle drops just pull over and pop the hood. 
Check the voltage at the alternator and at the battery. 
You want to compare the two.
I would also park in a safe place as you will want to check the voltage at the fuel pump harness in the rear hatch. Lift the carpet and using 2 paper clips (do not allow them to touch) measure the voltage.
Not uncommon for voltage drop here too.

I suspect your running issues are related to voltage, you could measure voltage at the fuse box to know if your have voltage drop from the battery. 

Not uncommon for water to drip on the fuse box. I just noticed it on my 85 Jetta. 

I have posted many times about upgrading the alternator, battery and ground wires on the Mk2 cars.
Fuel pump fix involves adding a ground wire from the connector to the black round cover.
You can also double up or replace the wires to the main pump using larger gauge wire.
Ground wires are very important to Digifant cars, especially in the engine bay. Make sure they are not broken.
Relays should be inspected for wear, they are easy to pry open.

You can also add an adjustable voltage regulator to the alternator. 
I had on on my 91 Jetta, but I'm currently using a VR6 120A alternator (ABA block and accessories running Digifant 1 head and injection). 
My 85 Jetta has a VR6 from a 96 Passat, CA smog legal swap done by me in 2000.


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## bretthbmx (Jun 20, 2007)

Eric D said:


> Based on your 1st post, I would carry a multi-meter in the car, when the idle drops just pull over and pop the hood.
> Check the voltage at the alternator and at the battery.
> You want to compare the two.
> I would also park in a safe place as you will want to check the voltage at the fuel pump harness in the rear hatch. Lift the carpet and using 2 paper clips (do not allow them to touch) measure the voltage.
> ...


Well I'm also running a mk3 alternator but a 90 amp. The idle doesn't raise or lower on it's own. It only rises when you unplug the CTS, like it's supposed to, plug it back in and it's fine. I'm leaning toward a bad oxygen sensor because the car runs fine with the CTS unplugged.

I also upgraded the ground and power cables too. All the grounds are good to go.


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## b5in (Sep 10, 2003)

****problem solved****

it was a bad o2 sensor so I had that replaced but it still was running rich and missing really bad so after replacing almost everything it could be it turned out the coil wire was bad :banghead:

so a new o2 sensor & new plug & coil wires and it's all good and I ran new grounds


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## bretthbmx (Jun 20, 2007)

According to my narrowband, mine runs really lean to where it hesitates.


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