Call it what you will, a complete tune-up should combine elements of preventive maintenance, adjustment and performance analysis. One of the main reasons people bring a vehicle in for a tune-up is because they are experiencing some kind of driveability problem.

Things like hard starting, stalling, hesitation, misfiring, poor fuel economy, or lack of power are seldom cured by a new set of spark plugs and a few turns of a screwdriver. Every tune-up should include a comprehensive performance check to verify that no driveability problems or trouble codes exist.

Another item that should be included is an emissions check. Thirty-five states now have some type of annual vehicle emissions inspection program, and all but two include a tailpipe emissions check. Most mechanics will check EGR valve operation, the PCV valve, and make a visual inspection of other emission control components and plumbing. But unless an actual emissions performance check is made at the tailpipe, there is no way to know whether or not the vehicle will meet applicable emission standards. An emissions check is a must.

Taking into account longer service intervals and reduced maintenance requirements of today's vehicles, a tune-up is probably only necessary every 30,000 miles, or once every two to three years. This is altered when a driveability or emissions problem arises that requires diagnosis and repair.

The best guide to tune-up frequency is probably the recommended spark plug replacement interval in a vehicle's owners manual.

Our list of items that should be included in a "complete" tune-up include:

• Replace spark plugs

• Replace rotor

• Check distributor cap (replace if necessary)

• Check timing (adjust if necessary)

• Check ignition wires (replace if necessary)

• Check ignition performance (firing voltage and ignition patterns)

• Check idle speed (adjust if necessary)

• Check choke (carbureted engines)

• Clean fuel injectors

• Check compression and/or power balance (identifies bad fuel injectors as well as compression problems)

• Check manifold intake vacuum (reveals exhaust restrictions)

• Check battery/charging voltage

• Check exhaust emissions (verifies fuel mixture, ignition performance and emissions performance)

• Check vehicle computer for trouble codes

• Install new air filter

• Replace fuel filter

• Replace PCV valve

• Check all emission controls (EGR valve, air pump, etc.)

• Check all vital fluid levels (engine oil, transmission fluid, coolant, brakes, power steering)

• Check belts and hoses

• Check safety items such as lights, wipers, tires (including inflation pressure), horn, etc.