Q: My car accelerates on its own when it's parked or sitting at a light while braking. Also, it stopped recently but it was misfiring

asked by on February 14, 2018

My car has been accelerating on its whether it's in park or is stopped at a light while braking. They recently replaced the gasket becaus the mechanic thought it was the gasket that needed to be replaced. However it began accelerating again recently and a little before this started happening, the car was misfiring every now and then when I turned it on. For instance, I would start the car and just a couple seconds later it would shut off and two lights would be on, a battery light and another light I can't remember which at the moment. Then when I would turn it on again it would stay on fine and during that time it was not really accelerating. It recently stopped misfiring and is now just accelerating on it's own, rpm will go up to 1 or 2 at the most when parked or at a light. Engine light just went on today so I will be taking it to the mechanic later for a diagnostic test since they thought it would be fine with the new gasket. Please let me know what you think, thank you.

My car has 144000 miles.
My car has an automatic transmission.

Idle Control Valve Replacement $146.15 - $920.51 Get a Quote

This may be a sign of a vacuum leak. High idle speeds or in some cases rough idle, stalling and hissing sounds are common signs of a vacuum leak. When a vacuum leak is present in an engine, this causes an excessive imbalance in the air/fuel ratio which creates a loss of power and causes the motor to run at a much higher RPM as a result of the increased oxygen present in the fuel charge being injected into the motor. This may also be caused by an idle control valve that may be sticking or failed due to old age or deterioration. I would recommend having an expert from YourMechanic come to your location to diagnose your vacuum leak as these can be very difficult and time consuming to trace.

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