Car accelerating on its own to 35 mph?

2008 chevy impala 3.5 flex. check engine light turned on for a misfire on cylinder 5 so I did a tune up, cleared the code, and the light turned back on. replaced the fuel injector, cleared the code, and it turned back on. Ran the code again and a new one showed up (p1174 fuel trim cylinder balance bank 1) along with the cylinder 5 misfire. Took out spark plug and switched it with cylinder 4 and regapped the plug for cylinder 5 (even though the plugs are supposed to be pre-gapped. Thought it fixed the problem.Couldn t feel it misfiring. Car was still idling rough and I thought it could be the engine mounds.(I know they need to be replaced). While I drove the dash lit up and said engine power reduced. Ran codes again and the same codes popped up plus another new one(app sensor 1 circuit low volt).replaced the gas pedal and the check engine light turned off by itself. Didn t have to clear it. Cleaned the throttle body and the maf( used designated cleaner for each). Drove it and noticed the car accelerated by itself. I drove it until the light turned on, ran codes and all but one cleared( p1174).was told it could be the TPS I replaced it and it still continued.was also told if you disconnect the MAF sensor and the car keeps running it s bad.tried it and the car kept running so I replaced that also. It continued.Thought maybe it s a faulty acc pedal so I swapped it for another new one and it s still doing it. It didn t start accelerating by itself until I replaced the acc pedal

7 Answers

  • Aaron
    Lv 5
    3 years ago
    Favorite Answer

    The APPS is probably a potentiometer which usually means as you depress the pedal the resistance increases thus lowering voltage and current which the computer reads and determines how much to open the throttle. It's possible that the aftermarket pedals you've probably tried are no good and a Genuine ACDelco part from a Chevy dealer might be the fix. It's also possible that the accelerator pedal position circuit has a short and the computer thinks the pedal is depressed when it is not so check the wiring harness under the dash for damage. If still no luck, it's time for a very good professional mechanic.

  • paul h
    Lv 7
    3 years ago

    GM has a bulletin for the P1174 code on many 2000-2008 related vehicles that can induce the issues you are having with misfires, etc.....need to clean or test the injectors. You can also try swapping #5 injector to another cylinder...clear the codes and test drive...if the misfire code comes back for the cylinder that the injector was swapped to, then likely the injector is bad. If it stays with # 5 cylinder, then you have other issues with that cylinder...vacuum /gasket leaks, ignition parts , etc..

    The acceleration on it's own could be due to a faulty APPS or it needs to be calibrated/relearn on some models...see repair manual or online sites on how to calibrate/ relearn the APPS to use GM parts. GM also has a recall on some Impala's for a bad APPS...they replace it at no charge or reimburse you if done already.

    P1174 bulletin.

  • 3 years ago

    New fuel injectors heed calibrating. They are not plug in items.

    Stop throwing money at the problem and take it to a real mechanic.

    A missfure is adding fuel to your oil and risking damage.

  • Anonymous
    3 years ago

    It is time to see a mechanic with a scanner/scope before you run out of parts to replace.

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  • 3 years ago

    Ok you sound hot. Get at me with your adorable car questions.

  • 3 years ago

    Ah, another "I'd rather spend $1000 on parts than $200 for a diagnosis."

  • Anonymous
    3 years ago

    Easy. You need new wiper fluid

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