I'm gradually sorting out my 98 XK8 Convertible and I feel that I'm almost there. Today I took my car for its longest drive since buying it. Over 3 hours.
I've been getting a random Restricted performance message which doesn't always appear and if it does, always disappears once the car is turned off. The most noticeable difference is that it is always accompanied by a red light and never a check engine light. Equally mysterious is that there is no loss in actual performance.

My investigations in JTIS show that there is only one DTC that relates to this combination of RP and a red light, and it confirms that there is no limp mode initiated. The DTC is P1250, which is for the Throttle body valve spring. I haven't found any definitive information anywhere on this DTC and consequently no solution.

As I don't really have any driving issues, I'm not losing sleep on this one but it would be good to clear this one up if I can.

Any ideas out there?

Thanks in anticipation!

Phil

 

I used to get this or still do I don't know anymore when I took my car on long trips up to Scotland. I would be driving normally and then for no reason I would get a restricted performance message, turn the car off and back on again and it would be fine sometimes. I cleaned the throttle body after getting this often in Scotland, the MAF and temp sensor. Repalced the thermostat as well. I've not had it since although I haven't been up to Scotland on a long trip in a year. The same would happen with the gearbox as well, it would throw a gearbox fault message but there was never anything in the codes. I wasn't revving the car hard or anything pretty relaxed driving but I suspect the transmission fluid is perhaps just getting a little too warm on a long journey? Or it's just an electrical gremlin where there is no actual problem at all.

 

Thanks for your reply Kuddlesworth. Were you getting the message with the red light or amber? Most of these sort of issues are accompanied by an amber light and a check engine light followed by restricted throttle. I have cleaned the throttle body and MAF sensor. I can drive for an hour with no indication or sometimes just 10 minutes. I too have a relaxed driving style and there never seems to be any particular thing I do to initiate it.

Thanks again for your input. I'll just keep an eye on things and see how it goes.

 

I have a 98 too. Does your cruise control work when restricted occurs? If no Easy answer, vacuum pipe disconnected to throttle body.

All is ok til you turn on cc, then approach a hill. Car tries to increase throttle with that vacuum- can't = problem. Resets with ignition cycle.

If yes, tell us. I have follow up info 4u.

John

 

Sometimes it was red othertimes it was amber. It was always weird, the gearbox fault message was also weird. I never got to the bottom of it but it hasn't happened since I last took it up to Scotland. When I go again this year I will see if it does it or not. One other thing it could be could be my intercooler pump not working because the fuse keeps blowing. Could be retarding the ignition too much although I wouldn't expect this after driving some 600+ miles.

 

Thanks John. Believe it or not, I haven't used Cruise control yet. I haven't had the right sort of drive yet. I'll certainly give it a try next time. I'll probably check the vacuum tubes anyway. I suppose a slight disconnection or crack might be the issue.
Phil

 

In case we hit the right solution, see post #5:
https://www.jaguarforums.com/forum/x...Cruise+control

John

 

This is an excellent post, as it seems the intermittent cruise/restricted performance/transmission fault codes are common.

I hate to admit that I've been ignoring the problem for several years as it doesn't seem to affect highway performance and frankly I've sort of given up on wrenching in favor of driving my zombie car, since I brought it back from the near dead.

The only symptoms I've experienced and will add to the discussion are that my cruise control and restricted performance issues don't show up if I get to the highway before the cruise stops working or the restricted performance light comes on. Stop and go driving triggers it. Sometimes the car cures itself on a long highway drive as well.

Don't know if you and the others are experiencing the same symptoms.

And one more symptom. The car seems to run better when the gas is really low.

I hope we can find a definitive cure to these issues. I'd gladly dust off my wrenches for an afternoon, to cure these annoying issues.

Good luck everyone!