My 2004 350z has been throwing a P0300 for awhile now and runs like total ****. It started not too long after changing out all my spark plugs. I have since changed both valve covers (noticed oil getting in spark plug tubes) I have checked for any vacuum leaks and I have checked every coil pack. My only though left would be a messed up injector. Is there anything else I should be checking or is it likely an injector that is messed up or clogged?

 

There are 2 coil pack plugs that are easily reversed, cant remember which 2 off the top of my head

 

4&6 but probably not the issue since 0300 existed prior to code toss and subsequent test n’ fix.