Skip the auto shop - Our mechanics make house calls

Q: P0300 Random misfire.

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Anti-theft - 2006 Chevrolet Colorado

Yes, the anti-theft could disable the engine given the right circumstances, however, I would recommend checking some other basic functions first such as fuel pressure since you are getting fuel from the pump but not to the rail. This is...

Q: Thermostat location.

The thermostat is located behind the outlet pipe on the front of the engine just above the water pump and pulley. The hose that hooks to the outlet pipe goes to the surge tank. Looking from the front the outlet...

Q: what would the cost be if we supply the radiator

Besides the 4.0 hours labor at your local charge per hour rate you will need to also supply the coolant for the engine and also the refrigerant to recharge the air conditioner after repairs are done. The A/C needs to...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.