Po300 At Idle

[gamc]

Ok how about some sage advice : 2004 Sierra,5.3 T 129K,wll maintained mostly hwy miles, new heads 25k ago at dealer due to the infamous porosity in castings. Recently developed an intermiitant misfire (popping po 300) ,idle rough, no apparent miss at speed. Dealer scan yesterday showed misfire at idle on #6 but it cleared off idle,injector good ,coil and plug good. Supposedly #6 is 20psi lower in compression than #1. I had the dealer stop at this point because they wanted to compression check all cylinders and didn't seem to know what I was referring too when I asked about a wet compression test on #6. If I have to go in the engine I'll get the dealer that did the heads to do it.

I really thought this was crappy ethanol laden fuel because the first time it did it was when I was running fuel from Va & Pa that was loaded with ethanol as opposed to what I get here in NC or Ohio. The truck also would throw a code randomly for the evap emmission system every now and then untill a couple of weeks ago when it did that with a po300. Now it just does the latter.

Geez I hope it isn,t a cam lobe. What is the best way to get to the heart of this quickly.

Any input appreciated

[8.1HD/ALLISON]

Take it to your trusted dealer and have them diagnose it. Could be fuel, spark, or compression related. Who knows? Thats why they call it diagnosis.