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2002 Chevrolet Trailblazer EXT experiencing PO300 and intermittent P0301 codes - troubleshooting guide

Model: 2002 Trailblazer Fault Code: P0301 Posted: 2006-10-27 06:39

I own a 2002 Chevrolet Trailblazer EXT with just over 60,000 miles on the odometer. Recently, I've started receiving both intermittent P0301 and a persistent PO300 diagnostic trouble code (DTC). After previously addressing the issue by cleaning fuel injectors, replacing spark plugs, and installing a new air filter, the problem has worsened—now showing a new PO300 code. The engine idles roughly, with the tachometer fluctuating between 500 and 750 RPM at idle, causing noticeable hesitation when starting from a complete stop. However, once I begin accelerating, the vehicle runs smoothly. Given these symptoms, I'm seeking advice on potential causes such as ignition coil failure, vacuum leaks, or injector performance issues. Any insights or recommendations for diagnosing this issue would be greatly appreciated.

Related fault codes
P0301
Comments (5)
Anonymous 2006-10-27 08:29

Possible root causes include engine mechanical wear, a vacuum leak, failing ignition coil, or dirty fuel injectors—these are common in older Trailblazer models with high mileage.

Anonymous 2006-10-27 13:30

I suspect the issue is related to ignition coil #1. After swapping it with ignition coil #4, both the rough idle and hesitation disappeared. This strongly suggests that ignition coil #1 is failing and contributing to misfires.

Anonymous 2006-10-27 17:23

It's worth noting that if the code shifts from cylinder #1 to cylinder #4, it could indicate a broader system issue or a faulty sensor reading.

Anonymous 2006-10-27 19:43

After driving aggressively for over half a day with no codes appearing—both in cylinder #1 and cylinder #4—I suspect that the injector cleaning or spark plug replacement may have introduced an air leak or misalignment, possibly due to loose components like the air box or poor coil sealing.

Anonymous 2006-10-28 06:55

No further updates yet; continuing to monitor for code changes and performance issues after driving under varied conditions.