I can put it in Cruise and it will slowly drop down in MPH. Diaphragm at Intake is good, Line going to Vacuum Canister is good but can't tell if it is good. I saw that there was a line going from it to the inside of the dash for heater was there. Could that line cause vacuum to be a loss for the Cruise. Dash controls don't seem to work to well. Thanks.

 

I too have a 98. This reminds me of when the vacuum hose to the throttle body came off.
Symptoms: start car, cc works fine, then you get to a hill, (this is where the car sends vacuum signal to throttle body to increase throttle), car decelerate realizes it lost control of throttle vacuum. Disables cc, amber alert lights on dash for reduced performance.

This occurred on my car because I needed new motor mounts. Movement of motor pulled hose free. So, as you can imagine I saw it happen 2 or 3 times. Always the same result. You reset the amber (was it red? I forget) dash alert with ignition cycle off on, but unless hose is reconnected = same cycle.

I couldn't tell from your description specifically how your cc falters, and I'm sure that you'd mention a warning on the dash lite/messages. But I figured we should acknowledge and cross this one off if its something else.

Photo link:
https://www.jaguarforums.com/forum/x...Cruise+control
John

 

Do you even get a message saying 'cruise control engaged' or something to that effect? If not, it may be the brake switch.

 

I haven't ever gotten a message on my Dash about the cruise.I can set the Cruise on level road and still losses MPH.

 

No messages ever. Only battery not charging but it is charging 13.6

 

I think the brake switch may be bad. There are two micro switches, one activates the brake lights and the other enables cruise control. They can be checked with a multimeter. Disconnect the brake switch plug high on the brake pedal. The two outer pins should have continuity until the pedal is depressed.

 

I have had to replace it already. It would cause the cruise not to work at all. This slowly loses MPH.

 

does the "engine fail safe" message come up in the vehicle display? If so, look for post on same. Cruise control drops out it the Accelerator Position sensor is not getting good electrical contact.