92 Jetta 1.8 hunting idle when warm

Hi everyone. I have a 92 Jetta (1.8 gas w/AC) that has recently started to hunt idle once it's warmed up. It's intermittent, but it's happening with greater regularity. Started a couple of days ago, during some really nasty cold weather up here in Canada, but is still happening.

When the engine is cold, it runs perfectly. As it approaches normal operating temperature, the hunting begins, gradually at first, worse as time goes on. I can keep my foot on the gas, and the RPM will stay steady. Acceleration is smooth. Only idle is affected as far as I can tell. Sometimes, even though it doesn't really "hunt", if I take my foot off the gas the RPM will drop to 100-200, then bounce back up to around 850.

I've done some research, and I think it's pointing to the Idle Stabilizer Valve. Maybe the cold weather made it "sticky" or something? I don't think it's an ECM problem (god I hope not, I can't afford that right now). I just want some second opinions, as I'm really not sure where to start looking for the problem.

Thanks! Chris.

Reply to
Your Name
Loading thread data ...

It's unlikely it's the ISV. There's actually something causing the engine to surge and the ISV can't compensate for it. It's more likely either the ground near the rear driver's side of the valve cover is frayed or broken, or you have a vacuum leak somewhere.

The reason it's noticable only when the car is warm is because that's when the feedback loop relating to the oxygen sensor starts working. Your engine is trying to compensate for something that's wrong. Note that this does not mean it's your oxygen sensor at fault.

Could also be an igniti>Hi everyone.

Reply to
Bob Hetzel

Thanks. I'll check that ground wire, and look for a vacuum leak if any. Good place to start, at least.

Yeah, I don't think it's ignition. When it's cold, or when I'm driving normally (ie not idling) it purrs like a kitten. It only acts up when it drops to idle.

It's unlikely it's the ISV. There's actually something causing the engine to surge and the ISV can't compensate for it. It's more likely either the ground near the rear driver's side of the valve cover is frayed or broken, or you have a vacuum leak somewhere.

The reason it's noticable only when the car is warm is because that's when the feedback loop relating to the oxygen sensor starts working. Your engine is trying to compensate for something that's wrong. Note that this does not mean it's your oxygen sensor at fault.

Could also be an igniti>Hi everyone.

Reply to
Chris

FWIW, you're in good company here. My '91 GTI 1.8 Digifant is doing the same thing. A few months ago my problem was that the idle would be a little high when returning to idle (say, 1000rpm instead of 800) and usually I could just let up the clutch and pull it down and then it'd be OK when I pushed in the clutch. I first cleaned the ISV and that made it worse (even higher). Then on a hunch I followed the reset procedure in the Bentley for the Digifant I unit (I have a California car and it's a Digifant I and can be reset) and that cured the high idle problem. It was fine for about two weeks and then it started this hunting thing and it's getting worse and worse. Since I already cleaned the ISV, I'm ruling that out. Let me know how yours turns out though (bad ground or vacuum) and I'll try the same. Apart from the hunting idle, it's otherwise smooth in every respect. I also did new plugs, cap, and rotor a few months ago so I'm sure those aren't the culprit.

Reply to
Matt B.

k&n or stock?

Reply to
news.verizon.net

Just an update... Since the -53 degree celsius weather has turned into much more normal winter conditions, the problems seems to have gone away. Didn't get a chance to really troubleshoot it. I did notice that the ground wire going from valve cover to body was in fairly rough shape, so I'm going to fix that. In the meantime, it's hard to troubleshoot something when there isn't an evident problem.

Thanks to the people that gave me some ideas. Chris.

Reply to
Chris

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.