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1999 GMC Sonoma P0300 Code: How to Fix Sputtering in Moisture Conditions

Model: 99 GMC Sonoma Fault Code: P0300 Posted: 2015-03-12 20:30

I own a 1999 GMC Sonoma with a 4.3L Vortec engine (VIN X). The vehicle runs smoothly under clear weather conditions, but when moisture is present—such as heavy dew, fog, or after rain—it begins to sputter and run roughly. Occasionally, the check engine light activates with code P0300. After driving for a while and allowing the engine to warm up, I can shut it off for 2–3 minutes and restart it successfully, at which point it runs normally. This inconsistent behavior is very frustrating. Can anyone provide insight or troubleshooting steps for this issue?

Related fault codes

P0300

Comments (3)

Anonymous 2015-03-13 06:43

Inspect the spark plugs, ignition wires, distributor cap, and rotor for wear or damage—these components are common causes of misfires leading to P0300.

Anonymous 2015-04-02 20:06

I recently replaced the distributor cap, rotor button, spark plugs, and plug wires. It ran well until today. After a rainstorm, it started exhibiting the same sputtering and rough running behavior as before. Are there any other potential causes or diagnostic steps I should consider?

Anonymous 2015-04-03 07:24

Check the ignition coil for internal shorting—look for signs of arcing or corrosion, especially when viewed in darkness. Also, inspect the distributor cap and lower plate interior for rust-colored powder, which may indicate internal degradation. Did you use AC Delco spark plugs? If not, this could contribute to misfires and trigger P0300.