PO304

Before randomly replacing any more parts take it to a shop that does proper diagnostics first and get an evaluation. In the long run that's often the cheapest route to go if you're unable to do that sort of diagnostic work yourself, and most of us aren't. I googled it and there are a number of things that could cause a P0304 code. It mostly indicates a misfire but doesn't identify why. That's where the diagnostics comes in.