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Q: I have an intermittent misfire - 2002 Pontiac Grand Prix

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My car is misfiring intermittently. It started out as nothing i noticed and the car would throw code P0300 which is random misfire. I replaced upper and lower intake gaskets, replaced map and MAF sensors, and cleaned the throttle body. Now I'm getting code P0403 which is the EGR. It misfires heavily when shifting when the throttle is wide open. Could a sticking EGR cause this? Misfire only occurs when at wide open throttle during shift from 1st to 2nd.

My car has 142555 miles.
My car has an automatic transmission.

A: Hi and thanks for contacting YourMechanic. ...

Hi and thanks for contacting YourMechanic. The EGR can cause a misfire if it is stuck open when the engine is cold or running at a lower speed. The EGR replaces some of the air with burnt fuel to help cool the engine down, but when trying to accelerate, the engine will starve for fuel and cause a misfire.

Remove the EGR, clean it out and put it back on and retest the engine. I recommend replacing the EGR. If you need further assistance diagnosing the misfiring issue, then seek out a professional, such as one from YourMechanic, to help with your vehicle.

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