Misfire Returns P300
 

I had a misfire problem last at idle last fall that I was able to work my way through and thought I eliminated. The truck never idled perfectly, but with 160K on it, I didn't expect it to, just wanted it to quit throwing codes.

Fast Forward. It has returned (warmer weather maybe part of the issue).

Although it sets a P300, I hooked up a tech 2 and can watch the misfire and it is predominantly on Cylinder 5, with some other cylinders randomly missing.

Here is the strange part that I don't understand. If I rev the engine up in Neutral above 4000 rpm or so, the misfire will go away for quite some time.

I also have a CMP reading of -16 degrees. Not sure I understand whta that is, but I had read before in other posts that it shoudl be +/1 2 degrees.

Any thoughts/help is welcome. Off idle, the truck runs quite well. Accelerates well, no stumble, no hesitation. Just at idle.