Mike, is the “both were open” condition correct operation so that if one holds vacuum, then it has a problem? Also, I’m assuming you applied vacuum to each one at a time and not at the same time.
Rog - I have no ‘insider information’ (factory documentation) but based on the fact my c.c. is AFAIK working then yes, I would say both open is normal if ignition is off. And I applied vacuum to the ports one at a time, with the other port open at first, then blocked with no change in result.
Thanks Mike for your speedy response. I’m gonna try your test tomorrow just to see if there is a different result on my system. If the result is the same, then it’s almost back to the drawing board. I say almost because I have a couple other paths I intend to try which I will document as they mature.
Some might say, “Why put energy into fixing something that is basically a luxury item?” I say, “Because a luxury car like the Jag deserves to have as many of her luxury systems working as possible.” Besides, I enjoy the challenge. 
Agreed.
And there you have it! A lot of folks don’t get this, but is a bit of the thrill of the chase, if you will. Plus learning for the sake of learning.
Well said my friend!
at the momenti i have not jet fixed the cruise control. My first priority is ABS.
But i will check for shure if the valve is clogged.
Returning on ABS problem, i found that if i turn on the car, sometimes the abs light stays on , but it is also possible that the light goes off. Driving, if i make a strong breaking the light often turns on, but not always, and if i break gently the light remains off.
I tried 3 or 4 strong braking on wet surface and a couple of times the abs worked perfectly (i felt the abs modulating the braking) but in other circumstances the abs was not working.
So, if even one time the system worket, i suppose that there in not m major fault in the circuit. What do you think?
My goal is to repair all the faults of my jag one day or another 
by the way i managed to repair the remote control and the lamp in the key
I tried my hand operated vacuum pump on the open port to the CC vacuum pump. No vacuum was maintained, so no blockage there.
I must say my CC has started behaving better as I’ve been using it while test driving, though it’s still not right. The only thing I can think to attribute this to is a sticky control valve that is getting less sticky with use. I bought a replacement vacuum pump and valve assembly on the cheap. Will post what I observe once installed.
Well, got the part. It was a used one since there are no new ones. Installed it and the test drive showed exactly the same symptoms. So, either the newly acquired module has the same “stickiness” as my original, or there’s something else to consider, most likely the latter. I also note the overall performance of the CC continues to improve as I drive the car, also with the new (old) vacuum pump. More thought is required!
Have you made any progress? While trying my CC, it worked good for almost 10 minutes, then it begun to increase speed again… I see that my cc performs better e if is use it… maybe there is a way to exercise the components… I think the previous owner has never used it.
You are experiencing exactly what I have been experiencing, though mine never holds speed for ten minutes - sometimes, maybe 3 or 4. I agree with your thoughts that maybe the components just need to be exersized. But which ones are the culprits? I surmised the vacuum dump valve to not be at fault since all the hard shutoff modes work. I believe the actuator is not to blame since its failure modes would seem to be such that the vehicle would decelerate, or the CC wouldn’t work at all. That left me blaming the vacuum pump/control module, so I replaced it with a used one (new ones not available). But the system behaved pretty much the same with it in the loop. Now it’s possible, if insidious, the new used pump/valve has the “stickiness” like my original has, and perhaps like yours has as well.
My plan is to purposely use the CC each time I take the Jag out to see if, over time, the situation improves. If so, well there it is. If not, on to electrical possibilities.
I’ll keep you posted on anything I stumble upon.
Rog
Rog, I previously provided the wiring diagram but I failed to include the inputs/outputs info, so here it is:
Depending on your aptitude / inclination you may want to investigate other possibilities like the input signal for road speed and the set/ accelerate signal from the switch.
Thanks Mike. When/if I get to this level of investigation, your info will be quite useful. Having the aptitude to debug these sorts of problems is not at issue. The inclination may be another thing. Have to weigh the trade between wedging myself under the dash and simply using the gas pedal.
Now, now, we have already discussed this…it is all about the challenge, the thrill of the hunt, so to speak…you want - no, make that NEED - to get that cruise control working! 
Of course, you are right, sir!