Hey Scotty,
I have a 2019 Chevrolet Silverado 1500LD 5.3L L83 with a 6 speed.
I recently got a code P0300 on my truck something about emissions it started to rough idle badly then like magic it went away. Truck has 110,000 miles on it. Have never changed spark plugs air filter is fairly new but haven't changed it in 2 oil changes or 6k mile intervals and I've been doing a lot of dirt driving. I also noticed it did it the next day after it rained and I drove thru mud (none 4×4). Code hasn't come back its been one week and 1500 miles later.
What can it be? Is it bad and should I have it checked out?
No more check engine light.
P.S. Transmission ran weird started hard shifting both on up and down shifts but that too went away after I turned of the truck and turned it on.
P0300 is Random Misfire Detected
We have a sticky here on codes and misfires under FAQ.
https://carkiller.com/scottykilmer/qa/misfire-4/
Also see here:
https://www.obd-codes.com/p0300
Since it went away don’t worry yet.
OnStar send me the diagnostic report by email I wish I could post a screenshot of it. But the engine light was flashing so I stopped immediately because I know when it flashed thats signs of really bad trouble. But my truck doesn't just have 110K miles. My truck also has idled a lot. When I mean a lot I mean like I've ran the engine for 2 weeks straight. Only turned off for refuel and at the end of the 2 weeks I replaced the oil. Did this for 7 months maybe more because I use to sleep in my truck. I use to do hotshot and towing a trailer everyday.
You can post pictures here! Upload the screenshot to imgur, then post the link here.