On my G 37 a PO 300 code showed up I put new plugs in it light didn’t go out I even when is far is clean the throttle bodies and the mass airflow sensor which I knew that didn’t have anything to do with the code, and then I put new coils in them the light went out. Got it the next morning. It was back on but they were cheap ones six of them for $180. They were called aceone and that didn’t fix it. You guys think it could be that they are the cheap ones I don’t think it’s compression because I get good compression. I just I had a little rough and don’t have as much power as it had unless it’s a vacuum leak or something like that I’m not sure hopefully somebody can help me out, or give me some advice. Thanks.

 

I had P0300 and no other codes, it was the fuel injectors. I made the very fatal mistake of installing eBay "refurbished" Denso fuel injectors. I got them from some merchant who claimed they were flowed balanced etc, pile of junk and of course they would not take them back. I put the original ones in with new o-rings and problem solved, had to clear the CEL. Lesson learned!