Preliminary Checks

1. Apply vacuum to cruise control servo at 3 inch Hg increments to a maximum of 21 inch Hg to test vacuum hoses for leaks, kinks or restrictions, repairing or replacing as necessary.
2. Visually inspect cruise control wire and ground connections.
3. If speedometer does not work, check vehicle speed sensor.
4. Check cruise control fuse.
5. Check cruise control servo linkage for restrictions or kinks.
6. If tap-up and tap-down functions are the only fault in system, replace cruise control module.

Fig. 1 Linkage Adjustment:

Fig. 2 Servo Adjustment:

7. If cruise control system loses speed while engaged, proceed as follows:
a. Check throttle valve cable, adjust if necessary, Fig. 1.
b. Check cruise control servo linkage, adjust if necessary, Fig. 2
8. If cruise control system surges while engaged, proceed as follows:
a. Check for adequate vacuum source.
b. Check cruise control servo vent valve for leaks.
c. Check speedometer driven gear for chips or wear.
9. On 1989 models, check resistance between grounds G131 and G250. On 1990 models with 5.0L VIN Y engine, check resistance between grounds G202 and G102. On 1990 models with 5.7L VIN 7 engine, check resistance between ground G202 and G203. If resistance is greater than .1 ohm, clean and tighten both grounds and the negative battery cable. If ground circuit is suspect, add ground strap between engine block and bulkhead.