Hi, I have 2012 G37 convertible giving p0300 and p0303 codes of misfire. I have new spark plugs, coils, and boots and cleaned both mass air flow sensors and still misfiring & getting these codes. Any idea what I can do to get my baby back to normal?

 

P0303 is number 3 cylinder. Could be an injector or something mechanical related to number 3 cylinder. Have you checked the compression on? Could also be the wiring to the coil or the coil connector.

A misfire could be due to a lot of things, looks like you started troubleshooting and removed a few variables already.

Do you have a local shop that specializes in VQ's?

 

Since the engine components are the same between all the models, it might be worthwhile posting this in the coupe forums (I'm assuming you searched already).

 

I also read about vacuum leaks - do you have any intake mods on the car?

 

Since you are seeing a misfire on cylinder 3, I recommend moving your new COP and plug to another cylinder and see if the problem follows the parts or stays on cylinder 3.

I put all new coils and plugs in and still had an error not turned out the COP to harness connectors were not tight on 2 cylinders. If the problem stays with the cylinder I would be looking at the engine harness.