97 legacy misfire

I have a 97 outback which starts up and runs fine until it warms up. After a few minutes it will start to misfire. Pulled a p0304 code, misfire cylinder 4. Any suggestions? The odd thing about this problem is that it only starts after the car is warmed up. I'm getting good voltage from the O2 sensors, fuel injectors, and the plugs/wires/coils are all new.

cylinder 4 starts to misfire intermittently after it goes to a closed loop, but it runs great in open loop.

It sounds to me like... ahh what the hell is that called, on old distributer cars its called the igntion module i forget what its called on newer cars.

I have a 1997 2.5gt too and I just fixed this same exact problem. There are 2 things it could be both of which you can check for with a compression check. First problem is the head gasket, after 70-100k miles they tend to crack and cause a small leak of sorts, but the second, and more likely of the problems, is that one of your valves or valve guides is messed up and are not sealing correctly making your compression drop. The fix cost me about $1200, good luck with it.