Here is the story: Few months ago car overheated on freeway due to faulty degasser tank. Fixed the tank and also replaced the water pump. After the car overheated it had a slight miss, the car sat for a few weeks before i decided it was time to fix it. Took the car to a buddy who works at Ford he ran it on the computer and found that cyl 5&6 were dead, low compression. Took the car to another buddy to work on it, pulled the head off and found 2 burnt valves and 2 guides were screwed. He put the car back together, it has more power and runs alittle better. The car still has a slight misfire, it threw 2 codes : po301 and a O2 sensor code, replaced O2 sensor nothing changed. My question is where to start next? should i have done both heads while the motor was apart? I'm starting to wonder if the back head has something to do with it? I don't hear the motor ticking or anything out of the norm, The rpm at idle is around 6-7 hundred range, lower then usual. The exhaust sputters at idle and sounds like crap. I also have a CEL flashing while it is at idle or sitting at a light for a long time. Any help would be great.