Cylinder MISFIRES are generally straightforward to diagnose...
But sometimes they're NOT!

This 2008 Pontiac G5 2.2L Ecotec is setting a P0300 Random Misfire DTC at 244k miles.

It runs a bit rough at IDLE, with an OCCASIONAL "hiccup" on Cyl 4...not a constant misfire.
Under LOAD, everything is smooth and PERFECT!

Obviously it already has brandnew spark plugs and coils.
What else could it be? Injector? Vacuum leak? Bad valve?

I have to pull out ALL THE TRICKS in my diagnostic arsenal to give the customer a 100% conclusive diagnosis. Even improvise a cool exhaust TAILPIPE PRESSURE PULSE test along the way!

IVAN'S PICO WAVEFORMS:
https://drive.google.com/drive/folder...

PHAD PRESSURE TRANSDUCER:
http://www.pinehollowdiagnostics.com/...

OTC 3398 Fuel INJECTION Pulse Tester:
https://www.amazon.com/dp/B0002SR5OO?...

TESLONG NTS500 DUAL CAMERA BORESCOPE:
https://www.amazon.com/dp/B07SQ4FLYX?...

THINKTOOL PROS: *****TOTAL $150 OFF!!***
https://www.amazon.com/dp/B08SWH2KP4?...

Enjoy!
Ivan