service engine soon and trac light come on embed go off at random

I've got a 99Pontiac grand am the trac light and service engine soon light come on and will go off and on and of
randomly. When they come on the car idles really rough, the car vibrates and shakes, three car when stopped
sometimes refuses to speed up and move, I've replaced the ignition coil the spark plugs and the wires the fuel find
the lights still come on and off. Since the fuel filter change its been driving much better and three idler is no where
near as bad, barley now but the lights still come on. On the car MD the code 304 comes up for a misfire on the 4th
cylinder just as randomly. It shows when the lights see on, and after a few passes on the MD the lights clear snag
the car drives like a dream, need advice