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2006 Grand Prix GT 3.8L Supercharged - P0300 Misfire, Hesitation & Idle Issues

Model: 06 Grand Prix GT 3.8 Supercharged Fault Code: P0300 Posted: 2011-10-09 16:53

My 2006 Grand Prix GT with the 3.8L supercharged engine is experiencing a persistent misfire (P0300 code) and hesitation during acceleration. The vehicle also misses when idling, and after releasing the accelerator pedal, it suddenly accelerates unexpectedly. This issue has been ongoing for about a month. I've already replaced the spark plugs and ignition wires, confirmed fuel pressure is at 60 psi, and checked that there's less than 1 psi flow through the upstream O2 sensor. Battery terminals are clean and tight. The engine runs smoothly when outside temperatures drop below 0°C. Additionally, I’ve noticed the ABS and traction control lights come on intermittently—though I suspect this may be due to a loose connection. The vehicle shifts harshly when the MAF sensor is unplugged, which suggests potential issues with airflow or sensor calibration. I'm looking for input on possible root causes related to ignition components, EGR valve function, or other system faults.

Related fault codes
P0300
Comments (7)
Anonymous 2011-10-10 06:47

Does your 2006 Grand Prix GT still have the remote-mounted spark coils and ignition module located under the hood? If so, that area should be a primary focus for diagnosis—corrosion or poor connections here can cause misfires and idle instability.

Anonymous 2011-10-10 08:11

There are three spark coils in this setup, and I'm unsure about the exact location of the ignition module. I plan to spend today testing with contact cleaner and dielectric grease on all connections—I'll update if there's any improvement.

Anonymous 2011-10-10 09:03

The spark coils mount directly onto the ignition module—this assembly is a common source of misfires in this model year, especially when contacts degrade over time.

Anonymous 2011-10-10 09:57

I removed the coils and found some corrosion on the contact points. I cleaned everything thoroughly and reinstalled them, but the issue persists. However, it's possible that the ABS/traction control light is related—could there be a shared electrical or sensor fault between these systems?

Anonymous 2011-10-10 11:47

Could a hot EGR valve be contributing to the symptoms? I notice slight misfires at idle and hesitation when accelerating quickly, especially under load. The vehicle hesitates around 4–5 psi boost pressure—this could point to EGR-related interference.

Anonymous 2011-10-10 15:11

An overactive or hot EGR valve can indeed trigger P0300 and cause misfires. Before replacing the EGR valve, try installing a pop-can gasket between the valve and intake manifold to block airflow—this should eliminate EGR-related interference. Does the valve get very hot when starting from cold? It shouldn’t heat up at idle. The ABS/traction control issue is likely unrelated; it's more probable that a faulty wheel bearing is causing the problem.

Anonymous 2011-10-10 16:08

I tried the pop-can gasket with no improvement. I’ve also cleaned and gently wiggled all ABS-related connections, and the warning light has not come back on—so it's likely not a wiring issue there.