Thread: acceleration and shift problems

Hello guys,

I have a 2004 grand prix with 103000 miles on it with the 3.8 engine. First of all the problem is that the car had a hard time to accelerate on load (its stuffering a lot over 3500rpm). After that when it pass from 4 to 3 (when it's close to 45 mph) if the car is on low rpm (1100 or close to that) and climbing a hill or just pressing a little more de gaz pedal the car will start to sometimes stuffering. But if i press more on gaz the car shift and there is no problems. if the trans change gear at higher rpm i will not have this problem.

Next i have no engine light but i alredy had a p0455 and p0496 and never came back and i did nothing to fix that (it's winter here and last time a had a p0455 the winter took it away and i dont know why) i have an engine support that is damaged (the engine lean to the left when you are in front of the car) and i found a 2 pin plug coming from the tranny that is unpluged. i don't know if it may have a link with my problem but now you know what the state of my car.

Next i cleaned the pcv valve and i replaced the 3 coils with the controller with a used one i had on hand. Its helped a lot on the accelerration problem but it looks like it could be better.

And now for the tranny i don't know what to do.. is it a problem with the engine, ignition, electronics or the tranny? a lock-up swich maybe?

thanks a lot for your helps guys

I think you need to separate the potential engine problems from perhaps the transmission problems. It seems you may have a combination of issues leading to what you are describing. I would do a full tune up plugs, wires, air filter, clean the throttle body, MAF, with the correct cleaners. Check the MAP sensor, EGR for clogging. Think about a fuel filter replacement. All the easy engine items that could eliminate the problem. Maybe replace the upstream O2 sensor. I would also go ahead and replace the PCV valve, I don't like cleaning it, replace it and also check the o-rings in the PCV housing sometimes they can be damaged with high mileage maintenance. This includes the o-ring of the MAP sensor.

Check the color of the trans fluid. Perhaps change it out and add some Lucas trans oil, I found it helpful, but opinions vary, and while there a shift kit would increase the life of the transmission. Just because you get codes pointing to one item doesn't mean that will or might be the culprit. I've had EGR codes show when in fact the problem was withe the MAP sensor. Also I've had bad Catalytic codes when the downstream O2 sensor was the issue. So start relatively simply and see if certain problems persist.

It sounds to me like you have poorly firing spark plugs. I'd replace the plugs and wires, if you haven't already.

thanks for the awsers guys!

i replaced the fuel filter, it did help thats sure. i cleaned the throttle body and the maf too. I will replace the spark plug they are pretty low quality ones. They have kind of a white deposit on it and i have never replaces the wires. Should i install ac delco platinium or iridium?

thanks!