I have an 89 GXL converted T2. Street Ported, open intake, 3" exhaust. Every once in a while I get an idle bouncing and I cant figure out why. TPS seems good, but maybe... When the idle starts bouncing usually it will fix if I turn on the electric fan. Seems weird, but does anybody have ideas what would cause this?

 

Could be the BAC adjusting for load when the fan is turned on.

 

vac leak.

 

I have tried tracking down any vacuum leaks. Doesn't seem to be any, but since this is sporadic, maybe there is one that just occasionally leaks.

 

When does the idle bounce. Warm engine? Cold engine? Braking only? Car not in gear?

 

mine only bounces cold. stupid thing. lol and i checked for vac leaks too. nada.

 

Sometimes a dirty throttle body will cause this among other possibilities.

 

my car has a lumpy idle due to running super rich at idle and it likes to oscillate. when i turn on the a/c or fan it tends to steady the idle out, especially the AC.

 

not to thread hijack - but how do I clean a TB?

 

Idle is always a little lumpy, but I figure that is due to the street port. The engine is usually warm when I get the bouncing idle. The TB has been cleaned when I had the engine apart for a rebuild. Most of the emissions have been removed, still have the BAC.