Some things never change, such as the need for periodic preventive
maintenance. But a tune-up is one job that's changed a great deal
over the course of automotive history. The outdated term is still
widely used by many people to describe a service procedure that's
supposed to make an engine run better. There's no absolute definition
of what exactly a tune-up should include, but most would agree that
it involves replacing the spark plugs and performing other adjustments
to maintain or restore like-new engine erformance.
The problem is there's not much that can adjusted under the hood
on many late model vehicles. Ignition timing is fixed and controlled
by the engine computer, as is idle speed and the fuel mixture. You
can still check base timing (maybe), idle speed and various emission
functions to make sure everything is functioning within factory
specs and are functioning properly. But there really isn't much
of anything left to "tune." Yet many motorists still want tune-ups
and believe tune-ups are an important and necessary service.