firstimport

Just bought my first Audi 90 (1988) about a month ago - big change from an F350 w/460ci - the gas was killing me. Recently the idle started going lopey, between 900-1100 rpm. Insanely cleaned the ISV with carb cleaner and WD40, replaced pertinent vacuum lines and T's. Funny thing, sometimes it idles fine - usually after start-up (cold), but when it gets warm, the idle goes lopey. Sometimes if you turn the car off when it's warm (ie. gas station), then start it again, the idle is normal for a while, then it goes lopey again, so the ISV must be working, right? Is there a way to bench test the ISV before dropping $250 on a new one? Should I be checking something else?

xr4tic

Probably get a better answer there.

Otherwise, I'd start with the usual suspects, vacuum lines, coolant temp sensor, bad grounds, etc.<ul><li><a href="https://forums.audiworld.com/9080/">https://forums.audiworld.com/9080/</a</li></ul>

Ghostfire

Is your idel just a stedy up and down swing from about 1000 to 900 or 900 to 800? When I say stedy I mean like a constant needle vibration up and down up and down. If so its probably your o2's. However, if its more like it goes from 1000 and dropes down to 200 or lower and then revs back up to 1000, about 10 seconds later only doing the same thing then its the ISV sticking a little. Also when you clean your ISV make sure you only clean the open half dont let any carb cleaner get down in there it will ruin the sensor. its best just to fill a small cup with carb cleaner then stick the ISV holes first about half way in the cut to get it cleaned remove it about an hour or two later and bamn nice work. It could however be a bunch of things though. My idel is wondering a little after the car gets warmed up as well. I think its my Coolant temp sensor the one that sends the signal to the ECU. Also one more thing the car will start up at 1100rpm but once warmed up it should drop down to 700 or so and stay there. Sorry for the late response I dont visit this side of Audiworld often im normaly on the 80/90 side.

Peace, Thomas