Ok, so I know that idle problems have been covered a million damn times; but......One question, I dont believe that my car has any vacuum leaks, the idle screw does nothing for the idle at all. When you first start the car it does the startup rev to around 3k, then once it is warmed it will sit at 1500 rpms. At times it will sit at 800 and bounce back and fourth between the two. At other times it will stay constant at 800. If it is idling oddly, I can put a foot on the brake and let out the clutch until I almost stall out the car, most times this fixes the idle back down to 800 rpms. At least until the next time light. I have no more guesses or anything of what this could be. Any ideas are welcome. BTW- Its an 88 SE N/A S4 manual.

 

if the idle screw on top of intake manifold does nothing your BAC valve is likely not working right. I would remove and clean the bugger, I hear its fairly common for it to get stuck.