Cruise Control Malfunction

[Keyav8r]

Rich told me he had experienced a problem with the cruise control (locking on and accelerating and not releasing) on the '91 I bought from him. So, obviously I had to see if I could replicate it and I did.

On the interstate at 70 mph, I switched on the cruise and the truck starting accelerating. Flipped the cruise off, kept accelerating. Stepped on the brake, kept accelerating. Pushed in the clutch and the engine revved way up. Had to cut the switch off and coast to the shoulder.

Re-started and the engine revved way up. Shut it down and removed the vacuum line to the cruise module, re-started and the engine revved way up. Shut it down and unplugged the electrical connector, no change (I'm thinking that's just for the indicator light?).

Finally disconnected the throttle cable from the cruise module and everything is normal (except the cruise still doesn't work correctly).

Does anyone have any idea how to fix this?

[HOrnbrod]

Sounds like the servo is engaging okay, but since it won't shut off electrically with the brake or stalk switch, it's sticking internally. AFAIK, you can't service these as they are sealed units. First make sure the servo cable itself isn't binding, then I'd replace the servo on the right fender well with one from the junkyard. Any servo from a 91-96 XJ/MY is a direct replacement.

[Keyav8r]

Would the sticking also cause it to accelerate? I'll have to get some of the vacuum tubing also as I broke the fitting trying to get the hose off. One more item on a short punch list.

[HOrnbrod]

Would the sticking also cause it to accelerate? I'll have to get some of the vacuum tubing also as I broke the fitting trying to get the hose off. One more item on a short punch list.

 

Yes, the servo is engaging electrically when you turn cruise on, vacuum is applied, and it pulls the throttle via the cable. Problem is it's not disengaging until you manually disconnect the cable. If the cable is okay, I don't see what else it can be except the servo.