Tune-ups vary between shops, but generally they consist of the replacement of spark plugs and other routine preventative maintenance to keep the engine running smoothly. Further maintenance included in some tune-ups involves replacing air and fuel filters and performing computerized systems checks.
Although many auto repair shops still offer tune-ups, the term has become somewhat archaic. Older engines needed regular replacement of a variety of parts but modern engines vary significantly in their maintenance requirements. Check your owner's manual for recommended maintenance schedules to avoid spending unnecessary money while still ensuring your car is maintained properly. Always ask about specific services included before taking your car in for a tune-up and check them against the manufacturer's recommendations.
Routine tune-ups should generally check the engine for wear and replace any hoses, filters or other parts that are worn. The PCV valve and engine ignition systems are some components that commonly need replacement. Battery function is also often tested, and the mechanic usually scans for fault codes to make sure there are no errors detected by the system.
Emissions testing is also usually part of a tune-up, especially in states that require emissions tests for vehicle registration. Older engines may need the distributor cap replaced. Modern tune-ups also often include a test or replacement of the vehicle's oxygen sensor.