All bank 1 cylinders had 79-81 misfires after 20min of idle, bank 2 had non. Cats are like 1year old hfc, downstream O2 is changed few times without result. Cleaned TBs and MAFs few times and nothing. Cant seem to find any leaks anywhere. Fuel trims are all fine. Planning to change upstream O2 but if that doesnt help, don't know where to look. Any ideas?

2008 G37s 6mt

 

I would try looking into the primary wiring of the coils on that bank. There's likely a common ground and/or splice that could be at fault.

Also, if you suspect the cat on that bank could be at fault, you can removed the upstream O2 on that bank and test drive, if your problem goes away, you've got a plugged cat. I've seen plenty of vehicles (non-Nissan/Infiniti) with severe drivability issues, no DTC's, and the cat(s) were clogged. In this case, I doubt it, but worth eliminating the possibility.

Before spending money on a new O2 sensor, which I also doubt is your problem, can you swap the O2 from the other bank into the trouble bank and vise-versa? I'm not sure if the part numbers are any different, I suppose the wires could be longer or something. Worth a try.

Good luck.