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1999 Chevrolet Suburban P0300/P0302 Misfire Fix: After Valve Job and Spark Plug Replacement

Model: 99 Chevy Suburban Fault Code: P0300 Posted: 2017-11-28 23:14

I have a 1999 Chevrolet Suburban with a 5.7L engine. After a recent valve job, I replaced the fuel injectors and confirmed good fuel pressure (65 psi). I also installed new distributor cap, rotor, crankshaft position sensor, and spark plugs. All components show proper hot spark when tested. The engine idles smoothly but begins to surge between 1500-2000 RPM after about 20 miles of highway driving. This issue resolves with heavy throttle input and the vehicle responds well under load. Diagnostic trouble codes P0300 or P0302 return when the vehicle is turned off and restarted. Switching spark plug wires has no effect. I've ruled out other codes, and spark plugs remain clean. What could be causing this intermittent misfire? Any suggestions for next steps?

Related fault codes
P0300P0302
Comments (6)
Anonymous 2017-11-29 09:14

Are there any additional diagnostic codes present? Can you describe the surging behavior more precisely—does it involve RPM fluctuations between 200-500 RPM? What is your current fuel pressure reading (in psi)? Do you have access to a scanner that provides live data for real-time monitoring?

Anonymous 2017-11-29 09:45

Only P0300 and P0302 are present. The surging occurs at steady highway speeds, with RPMs fluctuating between 1500 and 2000 RPM. Fuel pressure is consistently 65 psi. I only have a basic code reader that doesn't provide live data. Spark plugs appear clean and undamaged.

Anonymous 2017-11-29 10:01

When the vehicle surges between 1500–2000 RPM, does the speedometer behave normally? I suspect a TCC (Torque Converter Clutch) issue—can you verify if it's locking and unlocking unexpectedly? Try visiting an auto parts store that offers free diagnostic scans. These services can detect codes your basic reader might miss. Also consider adding a bottle of Seafoam fuel additive as a supplemental treatment.

Anonymous 2017-11-29 10:39

I apologize for the earlier description—upon reflection, this is more accurately described as a spark misfire rather than surging.

Anonymous 2017-11-29 11:36

No modifications have been made to the vehicle—stock setup. What type of spark plugs were used? Are there any aftermarket air filters or products like 'miracle magnets' installed? I recommend trying a free scan at an auto parts store, as they often provide accurate diagnostics without cost. Also, adding Seafoam fuel additive can help clean injectors and improve combustion performance.

Anonymous 2017-11-29 12:35

Thank you for the helpful suggestions—appreciate it!