Random misfire detected... What do I start troubleshooting? Already has new plugs and wires.... Kooks longtube headers, no cats.

 

From my experience it's normally a vacuum leak. That's where I would start. But there are tons of other things that can give the P0300 code or did it give a specific cylinder misfire?

Was the check engine light just on or was it flashing?

 

Past 2002 GM made it to where the code was no longer specific :/.

 

Check engine stayed on.
EGR may be deleted?

 

Maybe try the tune diagnostic forum???

 

P1133 Bank 1 Fuel Control Shifted Lean

And

P0300 Random Misfire Detected

 

https://ls1tech.com/forums/pcm-diagn...3-p1153-2.html