2007 lsj m62. Was fully bolted running fine. Swapped blowers for a stock one and put everything back to stock including injectors. Stock tune and all. At first car was misfiring all the time under light acceleration. Under heavy acceleration no misfire at all. Not the misfire has evolved to only 2 and 4th gears. 1st and 3rd are smooth with no issues. Has thrown a misfire code. Car bucks when it misfires. And it's inconsistent based on load and rpm. Help.

 

I would start with easy stuff even if you didn't touch them.

*EDIT*. I don't know much about the LSJ but if you don't have individual coils then just move plugs around.

Swap coil packs around and log.

Then if no change swap injectors around and log.

Go from there.

 

If it's only in 2nd and 4th, I would suspect something causing false knock that is causing massive timing pulling, but that shouldn't result in a misfire.

What codes did you get? I don't see how you can have a miss in 2nd, not 3rd, and then again in 4th... that's definitely the first time I've heard of that happening.