Q: P0300 Random misfire.

asked by on March 03, 2017

Having random misfire issues. P0300 code. I replaced all coils and plugs. It seemed to fix it for about a month, then it started misfiring again. So I replaced the MAP sensor, and the mass airflow sensor. That didnt fix it either. I can go a few days with no issues, then out of nowhere it misfires again and throws a P0300 code. I already paid Chevy 125 buck for them to tell me it just needed new plugs and coils. Any other small fixes I can try myself before I have to pay them again to probably be wrong?

My car has 104000 miles.
My car has an automatic transmission.

Without seeing the fuel trim readings in the computer to see if the engine is running too lean then it would be a guess that you have a vacuum leak between the mass air sensor and the intake manifold or one of the connections to the manifold. Have engine checked for any vacuum leaks. Replace the PCV valve and make sure there is no vacuum leaks.

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