Questions and Answers

Chevrolet C1500 Acting Weird Q. Vehicle runs good after I found several minor problems, Spark knock sensor, plug wires, distributor. cap and rotor. Now, when I set the cruise control, the truck begins to misfire severely. If I leave the cruise control set, the electric servo will attempt to open the throttle more to maintain speed.

The truck will backfire and miss until I disengage the cruise. There is no code set, and the "service engine soon" light does not come on during the misfiring. As soon as the cruise is turned off, the engine runs perfectly. Engine control computer or cruise control unit?

1990 Chevrolet Pickup C1500
5.7 liter 350 CID
Automatic transmission
94,000 miles
Throttle body Fuel Injection
P/S - A/C - Cruise control

Thanks,
Tim

A. Very weird problem! Try unhooking the cable from the throttle body that goes to the servo and see if it still carries on. Naturally the cruise won't apply the gas pedal but electronically, it should still have a load on the circuit. If so, I would look at the wires to the servo. Possibly a bad ground that is shared with the coil or ignition system?