Q: check engine light is on

A fault code p0304 is typically caused by a faulty plug or a failed ignition coil. If it has been quite a while since there has been a tune up done, I would start there. Many times a misfire can be remedied by changing the spark plugs and doing a simple tune up. If a coil has failed, it will need to be replaced. When doing an inspection, or when replacing the spark plugs, you can also look down into the tube that the coil sits on top of, and look to see if there is a build up of engine oil. If there is, then most likely, the valve cover gasket seals are perished, and the engine oil can keep the spark from the coil from getting to the spark plug. If you feel you could use some help with anything listed above, contact a certified mechanic, like those available at YourMechanic.com.