I need to find out what this error means and what to repair.

Question

I've done a full tune-up and replaced the mass air=flow sensor, but the code of PO304 excess emissions level of misfire on cylinder 4 is showing.   What do I need to repair this problem?

Answer 1

P0304 Misfire number 4 cylinder

This is a misfire code, some of the cause for a misfire condition are mechanical conditions, if not you still have a ignition coil that can  cause a misfire to a fuel injector that is not properly plugged