Nissan misfire issue

I'm working on a 2004 Titan with a misfire issue. I'm getting a P0302 code. i've replaced all the coils and plugs but it's still idling rough. I understand this is a common problem with these vehicles. the truck has 234k miles. any idea what it could be? also, it has JBA longtubes with the rear O2 sensors removed. it has not been programmed, the vehicle is completely stock. I just purchased an MPVI3 programmer but I don't want to do anything to the vehicle before i repair the problem.