Recap; Replaced stuck egr valve. Reassembled plenum/runners with new gaskets and torqued to spec. All vaccum lines accounted for. New plugs and wires. ( 5.7 tpi ) Fires up fine idles smooth until it hits closed loop ( 105 degree or so ) Starts stumbling and shooting unburned fuel out of the pipes. Idle gets progressively worse until I have to shut it down. Replaced CTS, O2, and just put in new ECM and PROM today. Fired up fine, continued to idle ok into closed loop. Thought problem was solved. WRONG! Took out for slow test drive around block. Seemed ok at first, but when partial throttle was applied, engine stumbled. Very low power also. But does run slightly better than before. Put old PROM in new ECM and ran worse (like before). So I am about ready to hang myself. So: engine runs better with new ECM and PROM but still runs like crap. Also, with the new ECM and PROM when engine stumbles it is NOT shooting unburned fuel out of the pipes. And all along I have not got one code thru this whole ordeal. Any help is greatly appreciated !!

 

Hook up a datalogging tool to it. This is absolutely ESSENTIAL. If you don't have one GET ONE. You have a laptop? good, if not get one. Get the cable from AKM electronics, $35 for the self assembled kit, programs to scan the data are free. Then tell us whats goin on inside your motor.

I'd say its your IAC motor. But thats before seeing any data.