Ive got an 87 gt and after u rev it up it will drop bach to idle and then start surging up and down...sumtimes it levels out and stops and sumtimes it stalls out...this happens regardless of temp and gear...where should i start to diagnose this?

 

start by telling us a bit more about the engine. Cam? any mods at all or is it bone stock?

Im assuming your still SD ?

Any check engine light ?

Check for vacuum leaks. Clean the Idle air control.

 

Sorry its sd and bone stock w/63k OG miles on it...

 

Funny thing is if i start it and let it idle its fine but soon as it revs up its starts this...

 

Start by taking you idle air control valve off of the throttle body . Check to see if it is clean where it bolts to the throttle body. If there is carbon inside the spray carburetor cleaner inside idle air control valve. Also use an old toothbrush to scrub where you've cleaned .Rinse the idle air control valve with carburetor cleaner and shake off excess . Try this first and that doesn't help then you may need to change idle air control valve.