Well, i can't really say in your case JDM as i do not have a turbo installed...so all my wiring and everything (save relocated and extended O2 sensors for my header) is stock.
Put the new coils in last Tuesday, put about 200 miles on it since...and it seems to be completely fixed. Mine too was temp related. The colder the ambient temp outside, the more often it would happen. Like i mentioned earlier, my situation was a perfectly driveable to 100% useless type of thing. That was what was giving away the two cylinders missing simultaneously for me. If this happened at an intersection or something, the car wasn't moving until it stopped missing, as it would barely rev in neutral, and letting the clutch out would instantly stall it. I was purposely not flooring it in these situations, as it was obvious something was seriously off.
It looks like i lucked out. I wasn't in the habit of letting it run when it would miss, no matter where i was i just turned the car off for 30 seconds or so and that would often 'reset' the coils or something and they would then work. I also don't have a primary cat, and i've seen the pics from other guys that literally had a 'chimney fire' after some missing because of fuel pouring into the primary catalyst and catching fire for a brief amount of time...ruining the cat. My secondary cat is so far away that this never happened, as the exhaust note and stream seems the same way it always has.
So the codes are all you can go by. In my case, which im nearly positive now was ONLY the coils...will ONLY throw the P0300 code. No other code thrown or pending each time i checked. OBD-II has no specific coil related code...so if you are only getting P0300, it may be one or several problems. The service manual states anything from coils, plugs, wires...to a blown head gasket as the culprit for that code. The EGR system, purge valve and purge canister, fuel sending unit/pump, fuel pressure regulator failure, injector failure, clogged fuel filter, and fuel system pressure problems can all also cause this, but some of them may trigger other codes at the same time. Vacuum leaks and things like that have a specific code too, which will often be triggered before its bad enough to cause heavy missing. My advice is to try and see just how bad the missing is in order to nail it down. Mine was definitely at least 2 cylinders. Many with a P0300 are getting 1 cylinder missing at a time (still gives enough power to move the car), its just that that its not the same cylinder over and over...which will likely mean its not a plug or wire, or even specific injector...and a problem of a broader system.
