Hello. As of late it seems my 2004 XJR is behaving badly. The vehicle isn't regularly used and is parked at my parent's home for months at a time. It sits unused, except for the odd occasion once every few months when they take it out for a warmup, or a VIP friend needs picking up at the airport. Well I guess disuse has caught up with it because now it seems to show a very serious problem.

So...Once the engine is up to temperature and highway speeds have been reduced to city stop and go the engine stops producing power. It won't completely stop, but it becomes evident immediately when the engine settles at around 800 rpm and won't move past 1000 rpm even if I mash the throttle. The Speedometer display shows a repetitive list of faults including "Engine Systems Fault" "DSC Not Available" and "Parkbrake Fault". If nothing is done and you try shifting back into drive the transmission will produce a very strong jerk and the vehicle will creep along at idle speed. Seems to me this only happens while slowing down, or stopped, not ever while speeding up.

In order to reset the car it is necessary to shift into Park, shut the engine down, and wait a few minutes before a restart. If I'm lucky the car will drive normally with no problems for a mile or so before it repeats the above scenario. It's exceptionally frustrating.

Any ideas I could look at? I was hoping for something simple like a loose connector, or a sensor replacement. The odometer shows approximately 90,000 miles, it's had a recent oil leak repair and oil servicing all done at Scott Jaguar in Charlotte, NC.

 

"Engine Systems Fault", "DSC Not Available", "Parkbrake Fault" mean only one thing...throttle body position sensor. Either replace the entire throttle body, or see if you can source the sensor by itself. If you are even the slightest mechanically inclined, you can do this yourself. Don't pay $1000s for someone else to do it. This is one of the biggest rip-off repairs for our cars.

 

Could it be a failing battery? You keep it on a conditioner?

 

By all means have your battery checked, but if it checks out fine, don't replace it hoping it will cure this issue. I did the same thing and wasted even more money in the end.

 

Thank you all for the good replies. Yes indeed, after reading your responses and a few other threads on this board, it seems the culprit is/was in fact that TPS. Today my dad and I unbolted the throttle body but failed to lift it off the engine due to the two cooling hoses permanently hose-clipped to it. Normally I would have just cut the two hoses with a sharp instrument but not knowing where they go to I thought it'd be a really bad idea. So reluctantly I just took a look around and bolted it all back together. Unfortunately for me during the replugging of a small two prong connector near the left side of the throttle body (driver's side) it pretty much dissolved in my hands. My dad carefully plugged the remaining part it in and taped it up securely with electrical tape. After it was all put together we started the car up and drove it around. Surprisingly the vehicle didn't throw up codes or go into limp mode as was the case just a few days ago. What gives? Do you think it may have just been a matter of an old "loose" TPS connector? It seemed to all be snuggled up tight when I first started looking around. Also, what could I do about that broken connector plug, are there any replacements I could purchase? In the mean time I've asked my dad to drive the jag and test it as much as he can stand during my absence. Hopefully that limp mode bug has disappeared, or at least we know to play with the plug to get the whole thing going again; at least for a while.

 

You are probably due a fuel filter change now too.