See Figure 1
In order to extract the full measure of performance and economy from your engine, it is essential that it be properly tuned at regular intervals. A regular tune-up will keep your vehicle's engine running smoothly and will prevent the annoying minor breakdowns and poor performance associated with an untuned engine.
A complete tune-up should be performed every 12,000 miles (20,280 km) or twelve months, whichever comes first. This interval should be halved if the vehicle is operated under severe conditions, such as trailer towing, prolonged idling, continual stop-and-start driving, or if starting or running problems are noticed. It is assumed that the routine maintenance described in General Information & Maintenance has been kept up, as this will have a decided effect on the results of a tune-up. All of the applicable steps of a tune-up should be followed in order, as the result is a cumulative one.
If the tune-up specifications on the vehicle emission control information sticker (located in the engine compartment) disagree with the Tune-Up Specifications chart in this section, the figures on the sticker must be used. The sticker often reflects changes made during the production run.