My92 caprice STILL surges when I start it up. When you first start it the RPMS will climb to about 1500 then fall to almost 500 before the ecm catches itself and prevents it from stalling by bumping it back up to 1500+/- and so on and so for about 1-2 minutes. Then the idle backs off to around 700 and stays there.

If you try to drive while its surging it will go, but even in gear it surges. Occasionally it will die as soon as you put it in gear if you try to drive while its surging.

If you stop the car after its warm and start it up again, it will not do it unless its been sitting for a while, then it does it only for a short period of time.

Im guessing it has something to do with being in closed loop (when the o2 is not on)

Things Ive done so far.

Rebuilt the throttle body, new IAC, TPS, fuel diaphram and gaskets. I reused the old injectors.

AC delco PCV

plugs, cap, wires

IF there is a vacuum leak, the only place I can think of it being is in the HVAC line back behind the firewall somewhere. I have new lines in the engine bay and the intake gasket is new. I hooked a vacuum gauge up to it and from the looks of it it doesnt have any vacuum leaks.

I tried another MAP sensor which was verifiedly good from another vehicle, no differance.

The EGR seems to be good, the idle gets weaks and starts to stall when you push on the diaphram.

I have another caprice just like this one but its a 93. It does not surge, I can swap parts from one to another. I just need some ideas.

 

IIRC there is a reset procedure for the IAC, to make sure that it's adjusted properly after either cleaning and/or replacement. It's been posted on TGO and it's probably in the FAQ forum. Did you do this?

The other thing is to make sure that receptacle in the TBI body for the IAC is also clean.

EDIT: not FAQ pages but Tech Articles forum...

http://www.iroczone.com/techartcleaniac.html