I'd actually argue that fuel filter and spark plugs are part of the "service" as they are consumable items that need to be replaced at regular intervals or as needed (same thing goes for brake pads/rotors etc) If I had to break it down, it would be thus: 1) Service = check and replace consumables if required (oil, oil filter, air filter, fuel filter, spark plugs, leads, distributor cap, brake pads) = things which keep the car running 2) Tune-up = Diagnostics check, adjustment of timing, injector clean/flush, ECU flash/reset etc = things which will make the car run "better", but usually no physical replacement of parts (unless something has failed). Or to put it another way, things which get "used up" are replaced in a service, things which "degrade" get "refreshed" at a tune-up.