91 Jetta crazy idle...please help!

This has happened twice in 3 days. I start my 91 Jetta, 1.8v, 5 spd, and my idle shoots up to 4000 rpm and stays there unless I start driving, press the gas pedal, and it goes away until I stop accelerating and it revs back up to 4000 rpm. Even if I'm stopped, in 1st, 2nd, neutral, it doesn't matter. My car has 170, 000 miles on it. The clutch may need to be replaced, though my brother, a well informed car kinda guy, tells me my clutch is in good shape. Anyways, so after about 8 times starting the engine, my idle eventuaLLY drops down to 2000 rpm, revs up again, then back down....It did this with me out of the car, in neutral....I can't see any visible problems...no cable sticking or anything. Yesterday I cleaned out the inside of the air vent with carburetor cleaner(my terminology is off, but hopefully you all know what I'm talking about) It obviously didn't help. So after it revved up and down, it eventually drops down to 1000 rpms, its normal idle, and everythings fine, at least with that particular scenario. So it seemed...I start driving and my idle sticks at 2000 rpm every couple minutes. Hopefully I've explained it well. I know a goood bit about cars, but I'm learning as I go. Any advice would be awesome. Thanks.

i had a similar problem as yours, except mine would drop to too low of rpms and then the engine would rev up to 2k then drop back down and sometimes drop too low and just die all together. There is a screw under the hood where you can adujust the idle RPMs, try to mess with that to make it right, this is on my auto 92 jetta though, so it may be different for you.

it could be your idle control motor dont mess with the screws ant the throddle they are set by the factory and that wont help you with the problem you have

You might want to try cleaning the idle stabilizer valve. It's the 1.5" diameter silver cylinder near the valve cover with the two large rubber hoses & one electrical connector.