Here is the deal.......

2007 GMC 3500 Savana

188k Miles

P0300 Miss Fire

New Parts

Coils
Wires
MAF
MAP
Plugs
Knock Sensor

Compression Check Good
Fuel Pressure Good

No other codes. Have a new Genisys Scanner

Symptoms:

Dead Miss Fires MIL Light flashes on idle runs like crap. Give it gas it runs great. We drive it all day no problems. Just at idlew at a light wants to stall.

I run a transportation fleet and this is one that is got all my guys stumped. So i told them I'm pulling in the BIG GUNS......

Any help is so appreciated at this point. I had a friend that currently works at chevy come by and he is at a loss also.

 

I'd guess IAT but thats built into the MAF on these engines iirc. Could be gunked up throttle body try spraying some intake cleaner through it and see what happens.

 

I know I cleaned my dad's maf and throttle body on his car, it had 170k+, and it was a completely different car. Check the maf, and the throttle body could have some build up on it from the awesome PCV system in our vehicles

 

I had to remove his throttle body, and scrape all the crap off of it, and then cleaned it with intake cleaner, that crap really gets caked on, and then baked on the tb

 

How about O2 sensors? They could be throwing the trims at idle off and it could be going to a lean misfire.

 

? Wouldnt there be a lean rich code of some sort?

 

unbolt the exhaust fromt he manifolds, start it up and see if it runs any better, sound to me like youve got bad cats.