Hyundai Repair Questions? Ask a Mechanic for Answers ASAP
After you replaced the cylinder 2 and 4 coils do you still have the same misfire P0302 and P0304 codes? And are those the only codes you have?
Can you hear any thing that sounds like a vacuum leak? Idle fluctuating that much has to throw a code eventually. It could be the idle air control valve also, which is part of the throttle body. If you can't hear any vacuum leaks, check the throttle body and see if it is dirty. If it is try to clean it out with some carb cleaner and a clean rag. If everything looks good, I would wait and see if another code comes up and go from there. Aside from doing a fuel injection cleaning there really isn't anything else.