I have a 2018 5.3 that’s been having a misfire issue. Truck has 67k on it, always Che fed the oil on time, and have kept up with regular Maintenance since I purchased ( Had 23k when I got it). I’m far from a mechanic but it seems and feels pretty obvious that that’s what it is. But I’m having some confusion with it.

after plugging it up to a diagnostic reader, testing each cylinder by turning off the fuel injection, and running multiple tests. I still can’t figure it out. Not only that but when starting it, on occasion, the rpm’s will go up to mid/high 1000 and drop to low/mid 1000 for about the first 30 seconds to a minute depending. I’ve never had this happen on a fresh start up only after I’ve ran it.

all the sensors are in working order. All the spark plugs seem to be in good condition, I’m just not sure where to look next. Any help or tips would be appreciated

 

Are you sure it's a misfire, and not just running crappy. A misfire should throw a code.

 

I had this same thing happen in my 07 Silverado. Rough idle then fine. Rough idle then fine. Never threw a code but once. Fixed the coil pack and the code was gone but still had a rough idle.

I tested in 2 different scanners 1 being snap on and another being whatever they had at Chevy, both similar results of showing a misfire but not showing on which cylinder.