P0300 OBD2 Code in 2002 Chevrolet Avalanche with 5.3L V8 Engine
I own a 2002 Chevrolet Avalanche equipped with a 5.3L V8 engine. Two months ago, it was repaired at a shop for two weeks after they discovered a wire causing the theft deterrent system to trigger. The issue has been stable until Monday, when I started experiencing rough idle, misfires, and stalling. I recently replaced the spark plugs with Champion Iridium plugs, but the symptoms persist. Now, the vehicle shows OBD2 diagnostic code P0300 — indicating a random misfire. When driving, it runs for about five minutes before feathering the accelerator pedal and then suddenly shuts off. Afterward, I must wait approximately 10 minutes before attempting to restart. Any insights or troubleshooting steps would be greatly appreciated.
For GM vehicles like this, always consider using AC Delco spark plugs. For fuel-injected engines, begin with a fuel pressure check — measure in PSI and then turn off the engine to observe how quickly pressure drops. Check the fuel pressure regulator (FPR) vacuum line: there should be no fuel present in that line. Also, inspect your spark plugs — are they wet or dry? Look for black or tan deposits, which may indicate poor combustion. Check the engine oil for signs of excess fuel contamination, as this can point to a fuel system issue. If no other diagnostic codes or modifications exist (such as remote start systems, aftermarket alarms, or non-GM parts), I suspect switching to AC Delco plugs will resolve the problem. PS: Always confirm whether the vehicle is stock — no aftermarket modifications such as remote starters or custom alarm systems.