[wagonman76]

My Celebrity has done the exact same thing since I bought it 7 years ago. Not as severe as yours, it only does it when the engine is stone cold and for the first 1/4 to 1/2 mile. Changing fuel tank/pump/filter didn't make a difference. Multiple spark plug/wire changes, crank sensor/ignition module replacement no difference. O2 sensor no difference. Alternator made no difference. Swap from 2.8 to 3.1 engine made no difference. Never any codes either. A coworker hooked it up to a realtime scanner and the good "128" number was about where it ran. I wasn't going to throw dollars at it trying to solve it (everything I replaced needed replacing anyway, and the 2.8 engine lost a head gasket when the radiator let out), so I just got used to dealing with it and it's just second nature now. But it never went away. All I can figure is it must be some sensor, or maybe even the ECM. I've got a hunch it might be the IAC, but unless I stumble across a free spare, I won't worry about it.

Edit: That reminds me, multiple bottles of Chevron Techron, plus this redline stuff. Also seafoam, and GM Top Engine Cleaner. Also changed the injectors with a newer used set. Tried a different TPS too once.

Would be nice to know what it is if you ever figure it out.