Very bad misfire, P0302

Year/Make/Model: 2007 Mazdaspeed 6 (imported from U.S. -09)
Mileage: 103,000mi
Location: Finland, Northern europe
Concern: Cylinder 2 misfire. Rough idle, but doesn't seem to misfire every cycle. Normal idle RPM. Very rough stuttering under acceleration, and blinking engine light (P0302). Engine light stays on after activation unless deleted. Cruising with constant rpm produces the same condition as idle (random misfiring, not every cycle). Starts up normal. FRP around 1600.
DTC's: P0302, cylinder 2 misfire
Modifications: none
ECU/Tuning Software: original
Tuner: -
Is the concern intermittent?: started intermittent, now constant
Can you duplicate the concern?: yes
Recent Repairs: new plugs after first DTC (NGK 3787, .031"), new coil (plug and coil also swapped between 3&2), compression tested good and equal on all cylinders, injectors cleaned + tested (resistance and flow), new Corksport injector seals, maf checked, replaced camshaft position sensor. Currently at the shop where they will check the PCM and exhaust sensor(?) on 9/13.
Correction: -

Might have forgot something from the list. Sorry for not having the exact details on everything or the freeze frame data right now, I don't have access to the car until 9/13. Please, if you have any idea lmk. Thank you.

 

Regap the plugs to .026-0.028" , .031 is too big.

 

Sure, but the problem started before changing the plugs, and stayed on the same cylinder. The OEM plugs have worked just fine so far, might upgrade to .028 later, but I don't have them at my local part store. Got any other ideas?

 

you dont need to buy new plugs just regap the ones you have. and yea the idea is to eliminate this oversized gap which could be a major contributor to the misfire. its free and easy should take less than 30 minutes so why not do it.

 

is p0302 the only code?

 

I'll take a look at re-gapping the plugs when I regain access to the car, but OEM plugs with a .003" gap difference in a spec car causing a progressive misfire just doesn't sound right, considering that the misfire began before even touching the plugs.

Yeah, p0302 only code, never anything else, couldn't even get it to hop to another cylinder (tested switching the plugs, coil, and injector.)

 

its nearly 20% over spec and known to be an issue on these cars.