long story short 2004 350z start missfiring/ p0300 i took the car to the nissan dealership they charge me but they didnt do ****. i replace the cats with high flow ones because they were busted, change spark plugs and coil packs at the same time the car is more stable but the p0300 and the missfiring continue,everything look normal, im gonna check the vacuum lines, and the injectors, does anybody had the same problem and can tell me there experience im just hoping isnt compression that it doesnt look like that my next step.
but if anybody had a same experience i would appreciate if u can give me your escenario

 

replace your crankshaft and both camshaft position sensors with either OEM nissan or Hitachi brand sensors (ONLY). Clean your MAF sensor

 

I know this is an old thread but I've had P0300 for almost a year. I've swapped out the coils, cleaned my MAF and sanded all of the plugs. No change. I need to check for vacuum leaks so I'm going to take off the engine cover and spray either carb cleaner or starter fluid. If theres a vacuum leak, you should see a change in rpm when the fluid gets sucked in. I hope to god it's a leak because I'm tired of chasing the problem.

PS: If you do this, be cautious. a buildup of spay hitting the spark plug well could potentially fireball. A spray bottle with water could be used as an alternative.