P0300 could be the plugs or may not be. I have changed my plugs since I was throwing that. Also changed my MAF sensor due pep boys saying it was the cuase. Both didnt fix it. BUT what did fix it was a fuel pressure regulator replacement. Easy install of $70 part after you get the tough bolts off the chamber. The part was $60 less than the MAF. But your talking about a lot more air flow failure than gas flow. I just threw this in there so if they replace something you still throw that code you what it could be. But I DID have rough idle, bad gas, and lots of exhaust.