I own a 2003 Chevy Silverado, 1500HD, 5.3L Vortec engine.

In the past few months my truck has been running rough and stumbles when starting and idling.

Anytime we’ve put a code reader on it, it comes up with the code P0300: random multiple misfire. We’ve run out of ideas as far as trying to fix this issue, any advice would be greatly appreciated.

We’ve done the following to try to fix the problem:

Replaced fuel injectors

Replaced fuel filter

Replaced spark plugs

Replaced O2 sensors

Found a leak in the vacuum line and repaired.

Battery has been replaced within the past 2 years

Cleaned the mass air sensor multiple times

 

Could be a bad coil or wiring. P0300 can be just one cylinder misfiring.

Could be a bad ICM as well, less likely. but possible.

I really hate an OBD P0300 that doesn't identify the cylinder, like vehicles some do.

 

I would check for vacuum leaks at the manifold to heads. If its leaking good time for knock sensors and the knock sensor too.