my idle is off on my 93 z 6spd. idles at like 1500 then if like few secons later goes down to 1200 then 1100. , is it my tps?? i have 58mm tb on it. and 3:42s in the rear. but i have the origional 93 6spd tranny. i dont know whats wrong, any ideas????

 

I take it you have tuning for the 58mm throttle body? The bigger tbs seem to cause issues sometimes. Other than that, it's gotta be something in the intake that's causing trouble. Does it surge or is it constant? You might have luck taking your throttle body off and cleaning all the passages out, mainly the ones for IAC.

 

Was the 58mm TB a recent install? Did it do this before the 58mm install? Did you try adjusting the throttle stop screw? Did you use a scanner to see how the IAC "counts" are responding?

 

My car is now doing the same thing.. I already replaced the IAC with a new gm unit and found (and solved) a major vacuum leak. I don't think I have any more leaks but I could be wrong. The idle used to climb when the car was rolling but now it falls.. only in really big steps.. from 2500 to 2000 really quickly and then from 2000 it hangs for a bit and then drops very very slowly.

I can't figure this out. The only other problem I'm having now is the PCV system (hose has a big crack in it so I put a sock over it and plugged the port on the TB).. I'm still deliberating over a breather vs. a new PCV hose.. but that's for another thread.

Anyways, let me know what you find.. if anything. Try looking for a vacuum leak also.. that can really mess up the idle.

 

If you don't also have a 58mm TB, your problem may not be at all related to the original poster's.