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I have a 2002 Grand Prix GT 3.8L. Just had the upper plenum and lower intake gaskets replaced, the valve gaskets replaced, a new EGR valve, a new radiator, new plugs and wires, and a new 4th gear shaft put in my transmission as the car was not shifting from 3rd to overdrive (this works fine now). The problem I have is that sometimes when I am in the middle of accelerating from a stop or as I am driving up an incline and slowly accelerate to maintain power, the car starts to accelerate in a very jerky or choppy way. I am usually depressing the gas pedal 1/4 to 1/2 way. The RPMs go back and forth from 1500 to 2500 as this is happening. But if I punch on the gas, the car will accelerate faster and not do this. It does not do it constantly. But it does happen every time I drive. My buddy is a mechanic for 20 years and he is the one who did all the work above. But he too has no clue what is causing this and is stumped. Ideas???? It is driving me nuts!


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Did this problem start after the repairs were made, or was all this done to fix this condition?


   
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Before. And it is not all the time. Only once in a while when trying to accelerate. I can drive 70 MPH nice and steady. I can accelerate nice and steady. Other times, I try to accelerate slowly and it is very choppy and jerky. the engine does not stall or choke out. But if I punch the gas, it goes just fine.


   
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What you are describing- hesitates from a stop and when up to speed, is a classic ignition problem. But since he replaced most all of it, that cannot be. I would assume he looked at the ignition coils while replacing the plug wires.

You may have a wiring problem. When you accelerate the engine moves and may be moving a wire for an injector, causing that cylinder to misfire. Your mechanic really needs to be looking at engien data while it is happening to determine what is going on. I have also seen a few times that a valve spring has broken, and sometimes will give a misfire, sometimes not.

All that said, the RPM's going from 1500 to 2500 is very strange. That tells me it is a transmission problem.
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Be sure to check the Similar questions down this page for more help.


   
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It's your torque converter. Replace it and she'll quit doing it. I had the same issue with my 02 Monte and we replaced it and problem solved. Good luck!


   
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