Mystery problem

JJ12345

I have a 99 Pontiac Grand am Gt 3.4l ...everything And I mean EVERYTHING from heads up including heads, all fuel system components,All sensors and even computer has been replaced with remanufactured one. Car starts and idles perfect ....As you start to drive will stumble,miss and almost stall ...release throttle goes back to smoothidle may do this once or several times .Once above 2000rpms car runs fine .Sometimes down shifting to lower gear (it is Automatic)will lessen problem ....I am at my wits end ...Dont want to sell car but have invested much money ....Also no check engine lights ....Anyone have any fresh ideas

imidazol97

To me this clearly is a problem that needs a Tech II hooked up to the ALDC and used to follow what's happening to the fuel mixtures and the adjustments the computer is making in real time. A professional who is used to using the computer with a car will get a sense of what the problem is.

Lots cheaper than hanging parts from the local parts monkey stores and guessing. A second problem to guessing is sometimes the aftermarket parts don't work right and generate their own problems.

A neighbor had a 3.4 in a Monte Carlo, IIRC. It was very sensitive to try to diagnose. My other neighbor is a shade tree mechanic and tried to help.

If it were my car, I'd take it to a GM dealer that has a tech who is older and has some experience under their belt with diagnosis. You may have a problem common to that engine OR you might have something unique. It would be worth the diagnostic time paid to get a good opinion and have a quality replacement part put on. Or it might be something like an EGR passage that gets blocked with crud.

JJ12345

Thank you for your input ....Car has been hooked up a couple different times but never driven as it was to see real time as it happening ....Will do that see what they are seeing ...Changed parts as Tech told me was wrong or if a code came up ...but your suggestion makes sense so thank you