Nowadays, the term "tune-up" actually refers to replacing and servicing the wear items in the ignition and fuel system. For example:
- The air filter and fuel filter will become less efficient and need replacing
- The spark plug electrodes will wear down and need replacing
- Because of oil vapors produced by the positive crankcase ventilation (PCV) system, the throttle body and fuel system will need to be cleaned and/or de-carbonized
The vast majority of the time, there are no adjustments needed (or possible), because the engine computer controls all the functions of the ignition and fuel system. The "tune-up" is often part of a large 30,000/60,000/90,000 mile service that includes inspections, and fluid and filter changes. These services are part of the manufacturer's recommended scheduled maintenance detailed in the owner's manual.
The modern vehicle should not exhibit any performance problems by the time a tune-up is due. If there are any performance problems, usually a Check Engine Light will illuminate, indicating that the vehicle needs some attention because it is not running properly and is polluting the air.