Cruise control troubleshooting
 

I’m driving my 92 XJS v12 from Miami to Boston this week. Cruise control is working intermittently. I can set it and it will hold for 5 to 10 to 15 minutes then it’s as if I’ve tapped the break. Does this sound like the dump valve failing? I can hit reset and it will come right back on again.

Here is a post I found with the same issue, might help.
as posted.

May have licked it , but I still need help. Little rubber seal on vent
solenoid missing, but I found it. The solenoids seem to be peened in the
body. Any suggestions on how to get them out without destroying the solenoid
in the process? I tried prying with a screw driver under the lip of the
solenoid but nothing moved. I think I’m asking, should I put it in a vise
and really put some pressure on it?

Byrnal Haley
https://forums.jag-lovers.com/letter.../e56c9b/45.png
Byrnal_Haley
May '00It works, probably better than before. Vent solenoid seal now glued back.
Many thanks to the list for your help and especially The Book and Kirbert
“what have you got to lose” Palm. Thanks again.

First, have you checked all pertinent connections, vacuum hoses, etc. ?

But before going too far into the weeds, let's identify which system you have.

A 1992 probably has the later cruise control system rather than the earlier "AE" system ....which is much more commonly repaired and discussed. The later system was made by Hella (or perhaps Kiekert? Can't quite remember for sure) and much less seems to be known about it.

Cheers
DD

I guess I need to do some research on this.

It worked like this for a few hours then quit altogether.