2007 Explorer 4.0 has intermittent misfire on #6. sometimes disappears after revving engine several times. code P0306 usually accompanied with P2135. No flagrant indications of head gasket problem, low compression on #6 but it runs & drives ok except for obvious misfire at idle. Have swapped injectors, replaced plugs, wires, coil pack, fuel pressure sensor, fuel filter, fuel pump, cam position sensor and checked catalyst converters, so hoping for sticking valve I poured some junk into tank hoping for a miracle. Ford still shows misfire intermittently.
Thoughts?? I know I am just throwing $$ at it at this point. Is there a possibility the ECM could be causing problem?

 

A misfire at idle that clears up with higher RPM could indicate a vacuum leak at that cylinder area,but if you have low compression there, it could be a valve related problem.
That could include cam and related parts. What are the compression readings for that and another cyl not next to it?

 

Thanks Hanky, appreciate the reply. Don't remember exact pressure #'s, had it tested by a garage. That mechanic said #5 was normal, 6 was half of 5 and he diagnosed a head gasket leak. The vehicle history involves extreme overheating requiring wiring patches and sensor replacements but it hasn't behaved at all like a gasket problem. I just parked after running some errands, it was missing so I put it into neutral and reved it up several times and the miss went away. Its done that before as I relayed previously but comes back. I was considering the PCM (Salvage) simply because its less expensive and time consuming than valves
Come to think of it, I only told the mechanic that I suspected a misfire on 6 so he only tested 5&6.