2000 Mercury Grand Marquis, check engine code 304.

4.6L V-8,200K miles. Started running poorly this morning, poor acceleration, rough idle, no check engine light until this afternoon. Checked code and got 304 misfire on cylinder four. Mass Air Flow Sensor hums from time to tme. Thinking clean Mass Air Flow Sensor, then maybe replace coil and injector? I prolly should buy the manual for this car too. Been just an awesome car.