2G Idle jumps 500 rpm when car gets hot

[Ludachris]

I haven't been able to find anyone else having this issue - ever since I got the car (97 TSi AWD) back from the smog check place (where they didn't even pop the hood) a few weeks back, I've had an issue with idle. It seems to only happen when the car is nice and warm, maybe a little hot. It will idle fine at start up and when the car is cool. But when it gets hot I notice the revs jump up 500 rpm to about 1400 when I'm sitting at a light. It might drop back down for a second but jumps back up and remains there. Then, after a few more minutes of driving, it will jump another 500 rpm to about 2100 rpm and hold there, occasionally dropping back down to 1400 and jumping back right back up and holding at 2100. Through all of this the car's factory temp gauge never moves from around the middle, so it doesn't look like coolant temps are getting too hot.

Is the ISC test on VFAQ something I need to do for this situation? Or would this be something different? I went ahead and made sure the BISS screw is set to about 2.5 turns. Not sure if all the 1g stuff applies though. I should probably get around to putting in the DSMlink ECU I have sitting in the garage to get some better diagnostics going. Still need to unpack after our move across the country.

 

[vr4scott]

I would atleast test the ISC to get a start on troubleshooting. Does this happen as soon as the car gets to operationg temperature or after you've been driving for a while?

 

[Ludachris]

I would atleast test the ISC to get a start on troubleshooting. Does this happen as soon as the car gets to operationg temperature or after you've been driving for a while?

I'll have to unpack my tools pretty soon here - garage is a mess after moving. It only seems to happen when the car gets hotter than normal operating temp, after I've been driving a while. But again, the temp gauge show normal temps. Igboost, I don't think it's a water pump issue or I'd see higher temps. It sounds like an ISC issue to me but it seemed like a strange way for the ISC to start going out. It's not erratic, it's steady and doesn't surge up and down like the normal problems people have. I'll see if I can find my tester.

 

[keith2g]

Definitely sound ISC related. Are you still running all emissions systems?

 

[delta448]

Check the TPS adjustment and your throttle cable slack. I think the idle switch isn't telling the ECU to idle.

If it's any consolation, I'm dealing with the same issue right now because I don't have any adjustment left in the throttle cable. I log ~15% TPS position at hot idle.

 

[Absit]

Check the TPS adjustment and your throttle cable slack. I think the idle switch isn't telling the ECU to idle.

That.

 

[romeen]

^^Agreed. This is fairly typical when the throttle cable is too tight. Try loosening it just a tiny bit.

 

[luv2rallye]

Agree with delta448. The Idle Position switch needs adjusting.