I had mistakenly posted this in an on-going ABS thread, but this is different.

I've been having a long nasty experience derived from a suspect throttle body assy (TBA) on my 2002 XJR, which has always included the dreaded "limp home" mode. You simply have no idea when and where the car will go into that mode. The damaged throttle Position sensor, i.e, Potentiometer (or pot) diagnosis make sense when they hear that, as long as I keep rpm's above 2000 rpm's the car runs fine, but as soon as I hit traffic or a red light and have to slow down (and with it bring the pot position into the damaged area), here we go again.

They (then called Briish Eurotech, in Lawndale, CA) had previously installed a used TBA and it worked for a few months, but it finally started showing its age and with it bringing the nasty limp home mode back. So, I went back to them (now called "South Bay British") and this time they wouldn't work on it, "unless you bring your own TBA". They wouldn't buy one and install it, so I purchased a refurbished unit from ASI and brought it to them, only to find that it didn't work. They were not hesitant to insist in that they did not want to work on this problem "because it's nothing but trouble".

So, I took the car to (Ian) Mitchell's in Culver City and they, too, said that the throttle body assembly from ASI was no good and recommended that the only way out of this one was just buying a brand new assy from the dealer. So, I bit the $2,350.00 bullet (over $3K out the door) and the car now runs just fine.

Ian said he has looked for a possible replacement pot all over the world for over ten years but he has not been able to find one anywhere, mainly because of the odd way in which these pots are set up.

So, being that this is a pot, it is no doubt a wear item that has its days numbered. My 2002 XJR has 95,000 miles and I would imagine that any XJR out there with these many miles is an obvious candidate for the infamous limp home mode due to the corrupted information that the ECU is getting from the damaged pot in the throttle body.

Too bad that Jaguar (even with Ford's R&D funds then) never resolved this issue in a more practical (cheaper?) way for XJR owners.

....Or, is there a better alternative out there that I just didn't know about?

Cheers,

 

Only thing I can add is that there is a good change the ASI unit was perfectly fine, it just needed to be adjusted first. There are two small screws, which when loosened allow the TPS to be twisted clockwise/anticlockwise slightly. Sometimes you need to give it a twist to get it into the range where your ECU will recognise it, rather than thinking it's also faulty.

 

I also noticed a lack of interest by the indies to get involved with used or "rebuilt" throttle bodies. I think they have been down that road which resulted in TBAs not working and un-billable hours. I did go the ASI route, replaced it myself and had no issues other than what Grandell mentioned about adjusting the TPS. My indie was very surprised it all worked out!

I hope you were able to return the one from ASI!

 

It does seem some have no issues with the rebuilds ..others do. I would like to know what ASI does to the sensor ... since it's not available separately .. they must somehow fix the old sensor.

It's also confusing as to the "adjustment" .. does ASI give instructions? When you get the new one from the dealer -- you don't adjust --- the screws are thread locked.

I agree. Jaguar should have a fix for this. It causes the cars to be viewed as problematic when it's a part that fails on many vehicles -- the sensors not the Tbody.

Back in the 90's I used to buy many Ford/Mercury vehicles -- the TPS was a common failure on them. I don't remember who made the part .... Denso is a big supplier to Ford ... I'm thinking maybe the Denso design may have been more prone to failure/problems in the 90's.

 

I think Jaguar would rather sell you a F type instead of fixing old throttle sensors. In the not too distant past there was a thread dealing with replacing the tps and I thought it a possible DIY. Can someone with a better memory comment?

 

I think that, if it was as simple as just "adjusting those two small screws", people with the experience of Nigel at South Bay British, or Ian at Mitchell's would be fully aware of it, as it is only obvious that they must've used ASI throttle bodies at some point before and, had they failed, they would've been instructed by ASI in regards to the necessary adjustment that just happens not not be required with new factory units.

BTW, I've heard that, if no new sensor pots are available, there's hardly anything they can do to a broken throttle body to call it either "rebuilt" or "refurbished, other than making them shiny and making them look like new.

Does anybody know what kind of sensor pot this is? Is it a carbon pot that gets pitted by any chance? There should be manufacturers out there who are able to fabricate specific carbon pots, or even wire wound pots.

 

It would be interesting to see what is inside of one.

 

From the Electrical Guide, it looks rather like the one in my car (an STR). It has 2 sensors with different characteristics and cross-references them, throwing a code / going into RP if they disagree.

 

do the xj8 and the xjr share the same throttle body, or at least tps setup? I might have to check the junkyard for a tb just to tear it down and see what this setup is.

 

There is an other thread floating around on the same issue.
Stumbled on it not even such a long time ago.
It got pictures and a serious technical discussion on the working, the problem of the wear inside ,and possibilities to repair the effected areas.
Adds very well to this discussion.
Tried to find it but short of time now, sorry.

But here is an other one, easy fix, for whatever it is worth: https://www.jaguarforums.com/forum/x...asy-fix-82342/