I have a 2003 Infiniti G35 M/T coupe with 185k miles, It is now making a knocking noise often while warm, no CEL, feels and sounds like a misfire, car shakes as well as the engine, gets to 0ish RPM but doesn't stall. When I rev the car it just sounds like a misfire but the knocking noise goes away and the car revs fine. Before this happened, I changed the crankshaft pulley seal, cleaned the intake filter, ported the upper and lower plenum, installed Z1 plenum spacer, and put a new serp belt on. It did sit for about 2 weeks if that matters. Could the car be running really lean/rich due to porting? I have a few other mods but nothing serious. (for the video)

 

Are you sure you didn't accidentally swap the coil pack harnesses?