Skip the auto shop - Our mechanics make house calls

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

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Car overheats after replacing hoses

The 3.1 engine is known for having air pockets after servicing the cooling system. There are several methods of filling the system to eliminate this problem: There are two “air bleeders” on the engine; one above the water pump,...

Q: Car misfire at idle.. changed plugs..coils..air fliter. gas smell and a miss sometimes. Any ideal was happening?

With the recent repairs made, chances are your issue is related to the fuel-system or a stubborn sensor that's on its way out. When was the last time you changed your fuel filter? The fuel injectors can also cause misfiring...

Q: trans hot idle engine comes on when i start the truck

Hi there. Understanding what causes the transmission hot idle warning light is critical to diagnosing your problem. The Transmission Hot – Idle Engine message can be displayed when the transmission fluid is too hot, which prevents the transmission from cooling...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.