99 Chevrolet Suburban P0302 Misfire: Diagnosis, Fixes & Real-World Solutions

My 1999 Yukon 4x4 with a 5.7L V8 and automatic transmission has the same P0302 code. I purchased it in January 2001 with only 16,000 original miles. The code first appeared during my first week of ownership. The dealer performed service up to 60,000 miles but never identified a root cause. They tried injectors, throttle body, clogged lifters, and weak valve springs—none resolved the issue. The engine has never been disassembled, burns no oil, and runs well otherwise. The code only triggers under sustained RPMs above 4,000 for about 15 seconds, typically during freeway passing or towing uphill. At that point, the light flashes a few times before stabilizing over subsequent start cycles. Since last year, the RPM threshold has dropped to around 3,000. I’ve replaced spark plug wires (a common fix), but it hasn’t resolved the issue. The original injectors and sensors are still in place. I’ve run extensive fuel system treatments with no change. I believe the oxygen sensor may need replacement at 100,000 miles—this could be my next step to resolve the problem. Thanks for sharing your experience!

If the spark plug wires are original, they should be a primary focus. A fuel injector leaking or bleeding off fuel is also a very likely cause of P0302 misfires in this engine model.

I’ve seen the same issue on my 2000 Tahoe—after reaching 87,000 miles. A mechanic in San Antonio reported that his vehicle had a similar idle misfire. He resolved it with fuel injector service. While I don’t personally feel the misfire, it’s noticeable under certain conditions. My check engine light is rare and predictable during normal driving, so it hasn't been a top priority. However, addressing it could improve efficiency and reduce emissions.

This issue should be prioritized. Continuing to waste fuel and increase emissions isn’t sustainable—especially with current fuel prices and environmental standards.

Due to today’s fuel costs, my vehicle has maintained consistent mileage (mid-16 to low-17 MPG on the freeway) for over 78,000 miles. I’ve tested fuel consumption across at least 20 full tanks with stable results. The vehicle has passed biannual California smog checks four times and consistently performs below allowable limits in all categories. The misfire only occurs under very specific driving conditions—such as sustained high RPMs—and is short-lived when it does happen. I’m taking a methodical approach, testing one component at a time during regular service intervals rather than spending hundreds of dollars on unproven fixes. I appreciate the suggestions and will continue monitoring other users’ experiences. Once resolved, I’ll share my solution here.

Problem solved—on my 1999 Suburban. After reviewing all previous repairs, I realized the original issue was not a misfire at all. The check engine light first appeared when a mechanic tried to start the vehicle while out of town. He replaced the spark plugs and crankshaft position sensor, but the sensor installed was faulty or low-quality. After replacing it with a high-quality sensor, the P0302 code disappeared after about 100 miles of driving. Thanks to everyone who offered advice—this helped me identify the real root cause!