I took it for a drive tonight when I got home from work. The ASC/Traction control lights were on when I parked it Tuesday night. After sitting for 3 full days it fired right up strong and there were no warning lights. Went for a 12 mile drive and the car drives great. I forgot how FAST it is compared to my current company car (2016 Malibu). It took the tires a good 8 miles to run smooth again; they seem to flat-spot so darn fast.

I have a suspicion that the codes are related to a throttle body issue that is currently extremely intermittent. My fuel trims have come down nicely so that problem seems to be largely solved, but it seems I still may have a throttle body re-build in my future.

 

Jeff,
I was hoping ABS module fix would fix it for good, till I open it I wouldn't know. What I fear the most is throttle body, because I had an engine limp mode happened once. Can this be detected by obd scan?
Maniqz

 

The restricted performance mode only happened to me once, and of course the ASC/Traction control warning came along with it. There was only one pending code and no engine light on. The code was p1121 on my regular OBD scanning equipment which according to many threads on here is a throttle body/throttle position sensor issue that usually requires a re-build of the throttle body.

The pending code went away the next time I started the car and for about 1,500 miles it hasn't happened again. My suspicion is that the occasional ASC/Traction control message and the P1121 code are symptoms of a degrading throttle body assembly. Luckily the re-build is not terribly expensive, but the car will have to be down for about a week while the throttle body is shipped off.

These are just my theories as to what's happening, it could still be any of a number of things.

 

A rare gem is very close to home lol.

1999 Twin Supercharged Jaguar Vanden Plas

 

Jeff,
I would assumed this throttle body issue has already been addressed on later models but it seems it's just a typical Jaguar symptom. I never get to scan my car when the engine limp mode happened so it's still a mystery to me but it's all similar to what happened to you. ASC and trac warning while on a limp mode and it also just happened once hope it won't happen again.
Maniqz

 

"Twin" Supercharged? Where do people come up with this stuff.

 

Probably because they see 'twin intercoolers' or know that the charger itself has 'twin rotors'.

 

I have the UltraGauge Bluetooth device linked to my phone so I can instantly check codes at any time. That's the only reason I was able to see the pending code like I did.

If you have noticed, I hardly ever post anymore. My poor beloved XJR just sits all week. I plan to drive it today to get a haircut, but this will be the first time I have started the car in 8 days! And to think I bought and fixed up this car to be a daily driver! Don't get me wrong, I love having a company car, but I miss my Jag!

 

it makes me think..."I'm selling a car and know nothing about cars so have fun with what I have or haven't done to it"😉

 

So I started it after sitting for 8 days and it fired up smooth with no warning lights at all. Drove into town for a haircut; car drives beautifully.

I guess based on that I can rule out the battery as a possible cause for the occasional ASC/Traction control message?

 

Little discovery:

With regard to the occasional ASC/Traction control message; if I hold the key in the start position until the engine has fully started the code never occurs.

If I turn the key to the start position and release as soon as the engine starts to catch I will occasionally get the warning lights. You know, it starts to catch and after I release the key it continues until all 8 cylinders are firing. After 5 days of sitting I started the car holding the key until the starter disengaged itself and no lights.

I have tried this several times and it seems to work. Maybe the power supply from the alternator is not fully steady until the engine is fully started? I am an amateur here so I am just guessing, but I thought I would share my findings.

 

So you are saying the system disengages itself, even holding the key?
Never tried that, guess I am old style.

 

I think starter motors have always had a "solenoid" that retracts automatically when the engine starts, protecting the starter motor. As a kid I always heard it referred to as a "starter solenoid". I have never really thought about it as an adult until just now.

I know if the starter did not disengage automatically my wife would have gone through many many starter motors! haha

 

Yeah, you might be right, but I never keep the key turned any longer than necessary, perhaps an old habit from my motorbike days, where you could definitely blow up the start motor.

On an other note, got bothered by a 'check rear lights' recently, and cleaned all power connections in trunk and engine bay as per your previous post.
Not really dirty, but shiny connectors have made the difference.
Again proof of how sensitive some of the control boxes are for power.

 

This is so sexy & close lol.

2001 Jaguar XJR(Supercharged)

 

2001 Jaguar XJR. 4.0 Supercharged. Clean car no issues whatsoever.

Can't be really true

I kind of like the x308 in white, and a light interior on an XJR is beautiful with the black accents.
Go go go for it!!

 

My 1st X308 love was White Onyx LWB, RIP in 2014 lol.

 

I like a white car, and I definitely prefer a lighter interior. Is it me or is there no price listed?

Also, it's hard to tell from the picture but it appears that car may be suffering from the faded wood problem not uncommon for the 2001 model year.

 

Harvest .... I never see you any more ....
Still having the XJR, or did you move on?

 

Going to see it tomorrow the seller has been a "riddler" on the phone w/ puzzling answers to certain inquiries, not certain if deception or ignorance. Whom knows how this may turn out.