Code 305

I have a 97 pontiac bonneville, the check engine light is on and its throwing a code 305, what does this mean?

Misfire in # 5 cylinder, p0305.

What is the mileage?Has it had a tune up?If not i would say a fouled plug or a faulty plug wire...

I agree with Jimmy. Try plugs and wires (as these are regular maintenance items), and if that doesn't help, the injector is probably bad on cylinder #5.