Hyundai Repair Questions? Ask a Mechanic for Answers ASAP
welcome to just answer and allowing me to assist you. Those two codes are cylinder misfire codes, P0300 is for a random multiple miss fire and P0304 is for #4 cylinder miss fire, If you want to go further would you like to do a phone call or more Q&A
Well if you still have a rough idle then that's why the miss fire . what you can do is erase the codes and drive it to see what ones come back. Then if it's showing a cyl missfire there are things you can do to pinpoint what it is causing that.Why don't you do that and we can proceed from there?