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.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: cylinder misfire

There seems to be a variety of symptoms going on at the same time. Addressing the ticking issue, it could be your lifters, and it could also be your fuel injectors. This could be part of the problem when it...

Q: Difficulty starting up after filling the gas tank

Hello there. It sounds like you have a few things going on. If there is no power to the DLC connector, then the code readers are not able to read codes stored in the ECU. The most common cause of...

Q: Possible causes of P0303 code 2009 Dodge Journey

Hi there - misfires can be caused by worn spark plugs, failing coils, or injectors dumping too much (or no) fuel into a cylinder, causing a misfire. Yes, this could be a failing coil. Swap the cylinder #3 coil with...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...