2000 Chevrolet Impala P0302 Code: Diagnosing Cylinder #2 Misfire and Ignition Module Concerns

Could you confirm if this is a 3.4L engine? Please specify the location of cylinder #2—this is typically in the front, passenger-side bank (first plug on that side). P030x codes indicate a misfire, which can stem from ignition, fuel injection, or mechanical issues. Have you verified spark at cylinder #2 using an AC Delco plug? What was the condition of the old spark plug—black, wet, dry, or tan?

Yes, it's a 3.4L engine. Cylinder #2 is located in the front passenger side, first position on that bank. I’ve confirmed spark at cylinder #2 using an AC Delco plug—blue and consistent. The old plug was dry and clean, having been replaced during a recent tune-up. I recently replaced all three coils (cylinders 2, 5, and shared coil pack), as the original coils tested weak. All new plugs and plug wires were installed. After starting the engine, it ran well for about three minutes before sputtering again and triggering P0302. A compression test showed all cylinders within spec, and vacuum checks passed. My next concern is the ignition module—would a failing one typically cause only cylinder #2 to misfire? I’m aware of its cost and don’t want to replace it unless absolutely necessary.

Cylinder #2 is indeed on the front passenger side. You’ve confirmed spark at #2—this rules out a faulty ignition module as the root cause. Mechanical issues have been ruled out via compression and vacuum tests. That leaves fuel injection as the most likely culprit. Please check for 12V and pulsation at cylinder #2’s injector using a Noid light—it's an easy tool to use. Try adding one bottle of Techron or Seafoam fuel system cleaner to see if it improves performance. If no improvement with the Noid light or cleaner, consider removing the injector for inspection. Swapping it with another known-good injector is a practical DIY test that can help identify the issue.

I confirmed spark at cylinder #2—blue and strong. The overheating stopped after installing a new 150-degree thermostat, though I’ve since switched to a 140-degree one for safety. The engine now runs cooler and more consistently. Using a Noid light today, I observed proper 12V with pulsation at cylinder #2. The injector O-ring was in poor condition—so I replaced it. I then replaced all three injectors with new O-rings to prevent future issues. Additionally, I installed new plenum gaskets and all new coils, plugs, and plug wires. After clearing the code, I drove the vehicle 15 miles under various conditions—hard acceleration, idle, A/C on, heat on—and no sputtering or misfiring occurred at any time. The engine ran smoothly throughout. I believe the issue is now resolved. Thank you all for your guidance. My next project will be my wife’s Envoy Denali with persistent ABS and brake light issues—another post to come. For now, I need to rest my old brain.

Using a 150-degree thermostat is not recommended—it may trigger P0125 (incorrect engine temperature), leading to poor fuel economy and rich exhaust conditions. The ECU expects the engine to reach a specific target temperature, which a 150°F thermostat does not provide. If this were a serious issue, GM would likely have designed a more suitable option for standard applications. Given that I live in a warm climate and have no winter heating concerns, the risk is minimal. However, I’ve verified with General Motors representatives and multiple mechanics—there’s little evidence of significant issues with 150°F thermostats under normal conditions. I’ve now switched to a 140°F thermostat for added safety.

I’ve switched to a 140-degree thermostat—thank you for the advice. The ECU doesn’t require a specific temperature; it only warns when temperatures exceed safe limits. If a 150°F thermostat were truly problematic, GM would likely not offer it as an option. I have over 40 years of experience in automotive repair and have consulted directly with General Motors engineers—there’s no evidence that the 150°F thermostat causes major issues under normal driving conditions. In my case, the vehicle runs perfectly fine and has not triggered any related codes. I appreciate your concerns, but I believe this issue is now fully resolved. The car was purchased three years ago for $200—so I’m considering selling it soon.