Mk2 Golf Idling too High

[Woogies]

So my '92 Golf GL has started idling at about 2000rpm consistently. It started about a week ago intermittently and now its idling at that speed all the time.

I've checked all the vac lines, throttle switch, oil cap, dipstick and removed and sprayed/cleaned out the ISV. Still the same.

So I found out today if I squeeze the vac line to the ISV (shown below) the idle drops significantly (500-600rpm). Correct me if I'm wrong, but doesn't this indicated that the ISV is not closing properly, thus allowing too much air through and causing the idle to increase? Also, when the ISV is disconnected and the car started there is no change (if anything the rpm rises a bit)

Does anyone have any help they can offer?

[Woogies]

So I found out today that it I rev it over 3500 rpm while stopped the idle will go back to normal. Maybe that will give someone inspiration to post an idea . She's probably going to the garage tomorrow, I'm getting sick of troubleshooting it; the problem seems to be evasive

[tom5191]

It could be your CTS (coolant temp sensor). That's usually a big idle issue with these cars. o2 sensor. You can also try adjusting the idle screw on the throttle body to see if that helps. Just remember how much you turned it in case that's not the problem and you need to put it back where it was.

Check this thread out of Vortex. VWVortex.com - High Idle

[Woogies]

Originally Posted by tom5191

It could be your CTS (coolant temp sensor). That's usually a big idle issue with these cars. o2 sensor. You can also try adjusting the idle screw on the throttle body to see if that helps. Just remember how much you turned it in case that's not the problem and you need to put it back where it was.

Check this thread out of Vortex. VWVortex.com - High Idle

I tried the idle screw, isn't much difference. Any idea of how to test the CTS to see if its working properly?

[tom5191]

You'll need a multimeter that reads ohms.
This'll help.
How to Test a Coolant Temperature Sensor | DoItYourself.com

[Woogies]

Originally Posted by tom5191

You'll need a multimeter that reads ohms.
This'll help.
How to Test a Coolant Temperature Sensor | DoItYourself.com

Well I bought the sensor only to go out and find that the one installed seems to be working fine

[tom5191]

Have you tried this yet?

Idle Stabilization Valve, once you've located.. do ao quick experiment.. start the car, let it idle, record the idle speed.. kill the engine.. pull the plug on the ISV.. start the car again,, has the idle speed changed?

[Woogies]

I have tried that.. The RPM actually rises when the ISV is unplugged.

Now if this means anything... I have two CTS (Presumably one for ECU and one for Dash). The blue one's resistance has changed noticeably as the car cooled down, the black as barely changed resistance. IE: Blue is at .48 ma and black is still at .18 ma.

[Woogies]

I tried adjusting the idle screw on the throttle body. It was originally about 2 1/3 turns out. After turning it in back 1 1/3 I can get the correct idle. Although I notice that it's bouncing very slightly. Although it seems to have fix the problem, as it's idling better than ever and seems to drive fine

Although the idle screw was very very easy to turn, I find it hard to believe it suddenly work it self loose. I hate to think that's not the original problem and I just jerry rigged it to work..

[tom5191]

It's weird, but the adjustment screw coming loose and even missing is kinda common. Mine randomly started doing it about 2 months ago and 1 full turn corrected the problem and she's been running better than ever.

[Woogies]

Originally Posted by tom5191

It's weird, but the adjustment screw coming loose and even missing is kinda common. Mine randomly started doing it about 2 months ago and 1 full turn corrected the problem and she's been running better than ever.

I remember reading a few forum topics where people mentioned that their adjustment screw had fallen out... I just kinda pushed that possibility aside because it was just way too simple . I'm gonna drive it a few days and see how she runs