My 98 Chevy Luminas service engine light came on and the diagnostics test read P0304 cylinder 4 misfiring. Would a tune up (change plugs, wires etc.) cure this or what should I do? Thanks

It may. My advice is "If a ‘tune-up’ is due or you don’t remember when it was last done, start there. You need to do that anyway and maybe you will get lucky, in any case it will make finding a real problem easier.

“Tune-up” no longer has a precise meaning. Ideally you would be following the instructions in the owner’s manual for maintenance. Not all cars have the same requirements. Generally if you don’t know when they were last done oil, fuel and air filters along with new oil is a start. Brake fluid and coolant change every 2-3 years and if an automatic new fluid and filter for the transmission about every 50,000 miles. Check PS fluid levels and washer fluid.

Put fresh plugs in. If that doesn’t fix it put new plug wires in. Remember to just do one wire at a time so that you don’t lose your place.