# 91 jetta idle problem



## ASB87 (Aug 9, 2009)

idles high sometimes, will jump high sometimes but be around 2k normally.. when i drive it.. sputters, then when i stop and push in clutch... it dies.. it had old gas with new on top.. burnt the old out.. 
TPS? or air flow sensor? anyone have any input?


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## ziddey (Apr 16, 2006)

*Re: 91 jetta idle problem (ASB87)*

No TPS unless it's a California model. Does your idle switch click?
Sounds like a vacuum leak / failing/gunked ISV


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (ziddey)*

i dont know what this is called... lol but..








the plug part that goes into the top of the engine, was split and hanging there, it was still connected but looked like a toad with it's mouth open. a big hole.. letting alot of air in.
i believe thats the problem..


_Modified by ASB87 at 5:40 PM 8-22-2009_


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## Fat Rabbit (Nov 18, 2001)

*Re: 91 jetta idle problem (ASB87)*

That is a breather valve -- replace the o-ring that it mounts in. That o-ring is the site of a lot of air leaks. People tend to overlook it -- at least yours is split badly enough so you noticed it. FR 
PN 028 103 500 -- less than $2 on line.


_Modified by Fat Rabbit at 6:49 PM 8-22-2009_


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (Fat Rabbit)*

replaced the part and still having idel problems, ive looked for air leaks but cant find anything! i dont know whats going on with this thing, any ideas? car will go from 500rpm's to 1.5k.... sometimes will sit at like 800ish.. 
ok also...
this thing here, when i push it in.. the idle goes down to normal..








also...
for some reason this hose is unplugged.. on my mk2 golf its hooked up.. but the PO seems to have re routed it../
here are some pictures..








the yellow dotted line is all one which on my mk2 golf isnt hooked all together..
--








basically.. the red x is connected to the orange x and the green x is going no where.. and where is hole is.. on my mk2 the red x was there../
idk this is wierd.










_Modified by ASB87 at 5:24 PM 8-24-2009_


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## ziddey (Apr 16, 2006)

*Re: 91 jetta idle problem (ASB87)*

OK, you have an idle switch as well. If you unplug the harness for the idle/wot switch, what happens to your idle?

as for the second pic, it sounds like the heater core was leaking, and the previous owner just bypassed it. no heat in the cabin.


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (ziddey)*

i unplugged the harness to the idle switch and it acted the same way.. but if i push in the idle switch.. it goes to normal.. its wierd.


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## ziddey (Apr 16, 2006)

*Re: 91 jetta idle problem (ASB87)*

you're pushing the WOT switch.
what happens if you unplug the MAF while the car is idling? It may stall, but I've been able to get it to somehow idle with no MAF signal.
How old is your CTS/HO2S


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (ziddey)*

im kinda newb with abbreviations.. and engines, whats MAF?
CTS/Ho2S?

EDIT: i figured MAF was on the intake box.. but.. the CTS?
Heated oxygen sensor.. is behind of the catalytic converter?
ALSO; my exhaust has 2 cracks in it.. behind both mufflers.. could be problem? or is it too down the exhaust?
_Modified by ASB87 at 12:33 PM 8-25-2009_


_Modified by ASB87 at 12:46 PM 8-25-2009_


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (ASB87)*

when i unplug MAF, car does die.. will start up run and die..
idk how old the CTS is..
i cant figure this out.. at all.


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## Fat Rabbit (Nov 18, 2001)

*Re: 91 jetta idle problem (ASB87)*

It looks like someone disconnected the heater core -- I've done that a few times myself -- you just loop the coolant and let the core sit in the dash -- it is a lot easier than removing the dash to replace the heater core. Heater cores go bad somewhat frequently. About $60 for a new heater core and three or four hours (maybe more) to remove the dash. install the heater core and replace the dash.
The microswitch switch on top of the throttle body you have been playing with and the switch on the bottom of the throttle body are to signal the ECU when you are at Idle (bottom switch) and at Wide Open Throttle (WOT) -- top switch. At idle the bottom switch should be closed so you should be able to check for continuity between the two male prongs of the connector to see if that actually happens. 
The switches are best replaced as a set. I like to remove the throttle body to replace them as it is easier to work on that way.
It is normal for your car to die when you unplug the Airflow Meter. 
Hope this answers some of your questions. FR
I am having a tough time following the vacuum line from the manifold to the brake booster in your pictures -- it would be a 1/2 inch dia. plastic hose -- I can see where it comes out of the intake manifold in one picture and the other picture looks like there is a yellow plastic end up by the coil. FR


_Modified by Fat Rabbit at 4:41 PM 8-25-2009_


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (Fat Rabbit)*

ok that did.. but also, will bad holes/crack in a few places in exhaust caiuse car to die out when you put in gas then let it off? it'll drop to like 300RPM's..
i cant find any air leaks.. that was only part of car i could think of being the problme.. the exhaust sounds like air sucks and bubblesputters...


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (ASB87)*

car drops so bad the battery light comes on and it almost dies out then it comes back to life.. jumpin up in rpms.. to like 2k


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## Fat Rabbit (Nov 18, 2001)

*Re: 91 jetta idle problem (ASB87)*

It depends on where the exhaust cracks are located. Leaks in the area from the exhaust manifold to the cat converter can potentially affect the O2 Sensor. You could unplug the O2 Sensor and see if that has an effect. It should connect in the engine compartment near the firewall on the passenger side. FR


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (Fat Rabbit)*

ok, i unplgged the o2 sensor, car doesnt want to stall out barely at all and it idles around 850..ish.. i drove it around the block and seemed fine.. other the the loud sucking sputtering sound from the exhaust... i need to change my plugs also..


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## Fat Rabbit (Nov 18, 2001)

*Re: 91 jetta idle problem (ASB87)*

That's good. That's where the car should idle 850 rpm or so. You should make an effort to get the exhaust fixed. At a minimum, carbon monoxide is a hazard to you especially during the colder months when the car windows are likely to be closed. You will have to take a good look at the exhaust system to see what needs to be replaced. If it leaks bad before the O2 sensor get that repaired first and then see how the O2 sensor reacts. 
The Bosch O2 sensor for your car runs around $100-120. There is a "universal" replacement available for around $40-60 -- it is for a Ford Mustang. you would have to cut the wires to the electrical connector and re-use the connector part wiring. The universal comes with crimp connectors however, I usually solder the wires together and heat shrink the connection area to assure a very good, long lasting connection. O2 sensors can be rugged to replace as they tend to rust in pretty good. There is a crow foot wrench that can be used to remove them. The tool costs about $25. The "normal" O2 sensor wrenches don't hold up well to a really stuck sensor. Most folks never replace the O2 sensors as regular maintenance. FR
The Mustang O2 sensor PN is Bosch 13913 (short wire) or 13953 (long wire). I have always used the 13913. FR


_Modified by Fat Rabbit at 7:27 AM 8-26-2009_


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (Fat Rabbit)*

the exhaust is cracked further down the pipe.. about mid car and last muffler. nothing up near manifold or the down pipe..


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## vr2jetta (Dec 16, 2007)

*Re: 91 jetta idle problem (ASB87)*

If you know the plugs are bad replace them first. Check that the throttle valve is adjusted properly too. On the throttle body there is a screw that 'appears' to be an idle screw...IT IS NOT! It is simply a throttle stop. If that has been tampered with, do the following. Back the screw off till it no longer comes in contact with the throttle linkage. Place a thin piece of paper between the screw and linkage. Tighten the screw till it barely squeezes the paper. remove the paper and turn an additional 1/2 turn and tighten locknut. Check the adjustment of the idle/WOT switches. Clean the ISV, replace the broken grommet to the PCV. Check your timing and idle. Idle is adjusted from the screw in the front of the TB. Turning the screw clockwise will decrease idle and vice versa. Good luck!


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## ASB87 (Aug 9, 2009)

*Re: 91 jetta idle problem (vr2jetta)*

i cant get the *BLEEP* spark plugs out, even with PB BLASTER!!


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