What did this "tune-up" entail? Plugs*? Cap? Rotor? Ign.Timing? Fuel filter? (the wires could be fine - test them at night, with a spraybottle of water...spray it on the wires w/ engine running...if you see sparks/arcs you need to replace)
*what kind of plugs? resistor/non-resistor? platinum?
Why dontcha pull each plug one at a time, and see what it looks like - take a pic and post if you have to.
Lotsa questions, I know, but how else to diagnose a car unseen and unheard?