New 88 Audi 90 Quattro and new to Audi's. Idle Problems...
 

I just purchased a 1988 Audi 90 Quattro. I am making a jump from owning a lot of BMW's over the last few years. I needed AWD and liked the Audi community. I have a problem with my idle. My idle will fluctuate between 1000-1600 and will continually go up and down. It only does this after the car has warmed up after driving. If I shut the car off it will stop and come back after I drive again. It is also idling at 1200 rpm which seems a bit high to me. I have taken the ISV off and I have the newer Bosch one. I sprayed a whole can of carb cleaner but it didn't make a difference at all. As I am new to Audi's I have no idea where to look. Any places common for vacuum leaks? Where else to look? Thanks.

vacuum leak, must cheak all rubber hoses, also there is a plastic elbow
 

behind the engine that can crack, also check the rubber hose under the intake manifold.

Also, check to make sure your ISV isn't sticking when hot...
 

I know you sprayed a can of carb cleaner in there... but if its sticking because of expanding materials, that could be the cause.

My ISV likes to stick sometimes... you can see the mark on the little rotary valve from where it catches on the edge of the valve window.

Re: Also, check to make sure your ISV isn't sticking when hot...
 

Anyway to fix it if it is sticking? Or does that mean I will need a new ISV?

Depends on what's causing the sticking.
 

Mine just needed to be wacked a few times with a big screwdriver... free'd up the stuck valve.

If it's a little burr causing the sticking, you might be able to file it off.