Well the cruise control on my 2000 xj sport has stopped, but its unlike all other threads ive read here. So i was on a cross country trip 2 weeks ago and my cruise would start losing speed from where it was set until eventually it wouldnt set at all. So i was thinking vacuum leak or my vacuum reservoir had gone bad. While out there i read on a thread that pulling up on the brake pedal may work so i tried that and it actually set but still quickly lost speed. After doing that twice it stopped working as well. So i got home (2000 miles later with no cruise...) and put in a new brake light switch and gave that a shot. Nothing. Picked up a vacuum gauge and pulled all the lines from the intake to the reservoir and checked them individually including the reservoir and the check valves. Everything works as it should and holds vacuum. My motor is pulling 17-18 in hg at the intake and if i unplug the reservoir and take a reading there its the same 17-18 in hg. After that i pulled the cruise control servo out and took it apart and checked all the o-rings and everything looked good. Im not sure if theres a way to check if that has gone bad or not though. So now im stumped... hopefully you guys can tell me where to look next or give me some direction. Thanks!
Oh and i pulled the switches off the steering wheel. Everything looked good there were no dirty contacts or anything.

 

If your TPS is starting to fail cruise control will stop working. I've had this happen on my 99.

Second is the clock spring going out will cause the cruise to not work. Though this way the crusie light on the dash will not come on. Where as a failing TPS the light will come on but cruise will not work

 

Okay Thanks! The tps looks original or atlest very weathered. The cruise light comes on every time though so ill look into testing/ replacing that!

 

I tested the tps and everything tests fine. It hasnt had any problem running or idling anyway so is there a way it could test fine but still mess up the cruise? also i cleaned the gray connector on the pcm and made sure that was fine since the wires that go to the cc servo are in there. I am also getting power to the servo when turned on and power to both wires that run to the pcm. Im so lost at this point...

 

So on the way to work today I turned the cruise on and pressed set. Nothing happened so I just kept my foot on the pedal and kept driving. But when I went to lift my foot the pedal stayed down! It was working. I tried all my controls and they worked but after I hit cancel I couldnt get it to set again... This is so frustrating. Anyone have any ideas where to look next? Its almost as if something is failing very slowly or I have a bad wire somewhere.

 

Yeah, something intermittent going on.
If the cruise light comes on all the time, that pretty much eliminates the cruise switch itself, not 100% sure about the clock spring though.

The clock spring could be doing a lot more than just illuminating the cruise light.
The PCM bus somehow has to get tied into the cruise operation.
When i get time gonna find my Haynes manual and look up the schematic.

Have you thought about changing out the cruise control throttle servo module as a last resort?
If you could get one cheap enough at a boneyard it might be worth a try.

 

Thats pretty much where im at right now. New online theyre about 90 bucks. ill have to check out some junkyards and maybe craigslist.

 

Don't know if any of this is going to be helpful or not.

My Haynes manual only shows a generic schematic for the cruise circuit.
And its only good for '89 to '96 years.
But it gives a basic idea of whats going on with the cruise function.
Unlike earlier years, the PCM controls the cruise function.
Apparently earlier years used a dedicated cruise control module.

It doesn't show the cluster cruise light but likely the PCM is turning that on via the bus.
Which kinda indicates the PCM is receiving the cruise enable from the steering wheel switch.

It shows 2 wires going straight to PCM from the steering wheel switches via the clock spring and a wire going to the brake switch then onto the PCM.
Basically 3 wires going to the PCM from cruise switches and brake switch.

Its looking like the clock spring, throttle servo, cruise switches or brake switch which you replaced.
No idea on how to troubleshoot or test the cruise throttle servo.

Here's what i'd do before throwing parts at it:
-Double check the brake switch connector for corrosion or spread pins.
-Double check the cruise throttle servo connectors for corrosion or spread pins.
-Check and/or redo all the grounds under the dash and in the engine bay especially making sure the cruise servo has a good ground.

These are long shots but worth an easy try.
-Sometimes but rarely a fuse will develop a hairline stress crack causing unexplained intermittent problems.
'Replace' the cruise servo fuse, don't just look at it or test it, replace it.
-Make sure none of the cruise control buttons on the steering wheel are sticking.
Had this problem years ago where soda got sprayed on the steering wheel.
Cleaned it up but later on enough of the soda got into the switch area causing sticking and problems.

Once fixed, let us know what you found.

 

Thanks for the info! Ill have to start cleaning grounds this weekend. Ill post what happens when i figure it out

 

Also, check any connectors leaving from the steering wheel column.

 

So i checked all the grounds and made sure everything was good and clean and still nothing. So on saturnday i went to a boneyard and picked up a new cc servo. Plugged it in and hooked up the cable and first press of the set button it pulled the pedal down by itself and worked. So i guess it was slowly dying. Thanks for all the help.

 

Great!
Thanks for the followup!

 

Adjust the steering wheel with the lever on the column. We had a problem in our 95. When I used the XJ after my son and adjusted the steering wheel, the high beams would not work. So when I used the jeep, I left the steering wheel position alone.