Engine misfire

I'm a new member to this forum and the owner of a 91 850I. The vehical has 174,000 miles, the engine just statred to have a misfire. I checked the plug wires, cap and rotor, they seem to be fine. When the car is started I can smell unburnt gas from the exhust. Could I have a bad plug and is there any way to isolate to determine if one or more are bad.