misfire problems

Ok.. it's not a SVX, but it does employ direct ignition. It is however, a Subaru.. a '91 Legacy wagon GT Jspec, with the 2.0L turbo engine. I have been having a misfire for sometime, but only on occasion. Recently, it has been getting worse. Mostly happens when it is good and warm, and when I come to a stoplight and idle. Sometimes, when I floor it, I can feel one cylinder not firing correctly. The plugs and coils were replaced(yea.. thanx a LOT Subaru.. it DIDN'T fix the problem).. and I'm not sure what to look at, cuz I'm not used to direct ignition systems. Any thoughts on how to trace this down?