Idle bottoming out

problem with a 91 AWD turbo. i have read a lot about problems concerning high idles, but my problem is that it cuts out sometimes. not every time i start the car, but most often when it does happen it is after i haved turned the key over and it comes back down to idle . . . cuts right out . . . sometimes after backing up. i dont think its related to a clutch problem because it will cut out even when ive thrown it in neutral and try to let it idle that way. any suggestions? it happens in both cold and warm weather. after the car has been running for a few miles though it almost never cuts out. usually when just starting it up. just changed plugs, wires, air filter, fuel filter, pcv valve.

Check the coolant sensor, make sure the connections are good and clean the throtle plate with a good cleaner.

If its not the coolant sensor, check the ISC motor

Could be ISC as talon007 said. Usually that will give you more obvious issues and it will do it all the time. Is the FIAV (fast idle air valve) working? (is idle higher when cold) Try dissconnecting the battery, waiting a few mintues, then reconnecting. This will force the ECU to reinitialize the ISC. Since its an open loop stepper (no feedback/encoder to relay its position) it can sometimes become out of synch with the ECU. After the car is running for a bit the ECU will learn where to put it, but on startup it assumes its centered, so I wonder if this could cause your problem. Try it out, since its so simple to reset the ECU anyway.

I'm having idling problems as well; GSX Racer, maybe you could help? My bird idles like I have really lumpy cams. It idles normal but "hunts" betweent 600-700 rpms without stalling. I can run a/c and drive the car normally and it doesn't do this all the time...should I just replace the isc motor? Is there anything else it could be?

For those symptoms I would check for intake leaks first. See the leak tester vfaq at www.vfaq.com. Cost 10 bucks, and takes a few minutes. The bad ISC will usually rev much higher when its surging...

I'm going to make a trip up to home depot to get the parts this weekend. I'm also going to get a can of carb cleaner and spray the crap outta the isc motor- that might work, at the very least I can prolong its lifespan. My coolant light stayed on for a split second this morning, now I have to check the sensor. God help me when I start modding this car