I believe my throttle position sensor is failing on my 4.0L 1998 XK8. Symptoms include slight surges while cruising at steady speed, random engine stalls when coming to a stop and sluggish acceleration. The only parts I have found online so far have been for the 1999-2003 model years. Is there a difference in the sensors after 1998 or will the ones I found work OK? If not, what part number should I be looking for?

Feel free to let me know if my diagnosis is incorrect or needs further research.

 

The AJ26 and AJ27 throttle bodies are VERY DIFFERENT.
Don't know about individual components but you might try a different throttle assy?

Can you monitor DATA from the ECM?

MAF and TPS are things to concentrate on.
I forget how many parameters are available for DATALOGGING but many 'scanners' can watch sensors related to the engine.

I have a simple $100 OBDII device that can read data in 'real-time'.

There are plug-in devices for 'smart-phones'?

 

I have two OBDII readers, one does do realtime data but has trouble reading the XK8 (does OK with my XF). I'll try your suggestions and see what I get.

Are you saying I could swap to the newer throttle body if I cannot get a part for the AJ26?

 

No idea is if the TPS is the same for the AJ26 and AJ27?(throttles are DIFFERENT)

 

Update: My Topdon Artilink 600 scanner reads live date streams, but not for my 1998 XK8. BTW no codes are showing with either of my scanners. Tried to contact Topdon but no reply as of yet, plus I have an Apple laptop and it seems their software updates only use Windows.

So back to square one. I'll see if any shop near me can diagnose and start looking for a throttle body assembly (gotta be cheap, right?) just in case. Prefer not to throw parts at it without some idea that is what it needs though.

Anyone using a 1997-1998 compatible scanner for live data please let me know what you have. Something under $200 would be ideal. @motorcarman ?

 

Jaguar had a Good Idea and made the TPS on our AJ26 a Hall-effect device which, in theory, won't wear out.
...then completely negated the value of that by using mechanical potentiometers for the pedal position and 'mechanichal guard' sensors
These are both made from high-grade unobtainium, AFAIK.

The throttle body for AJ27 is a completely different beast. If you were to swop, you'd need to take the later ECM and then you're into problems re the different VVT, etc.

I dread the day when this happens to mine.

 

Thanks. Yes I'm starting to realize the joys of having one of the earlier models. I am finding some 1998 TPS units for the XJ8, so now trying to decide if they are compatible with the XK8.

I did find a local junk yard/breaker that claims to have a used one off an XK8. Will look further into that solution.

 

Which suggests the TPS itself is unlikely to be the culprit? Wasn't there an issue on the earlier cars with the connections to the TPS failing?

It would certainly be a good idea before trying random part swaps to have a look at the live data - with the right scanner you can get the accelerator position, the commanded throttle position and the throttle position sensor position, as well as the MAF reading. With an ordinary scanner (such as Torque) you can get the MAF reading and the throttle position, but nothing else to do with the throttle/pedal, so quite limited use, but still better than nothing.

 

you can get global obd pids with a $5 elm327

launch and topdon have problems with the aj26/27 ecms and can’t connect over 9141 global.

 

After some research I am looking at the Innova 5310 scanner. Realize there are some solutions that are cheaper, but you really need a decent one for these cars. Plus the local mechanics that can do Jags want just about the cost of the scanner to tell me if there is any issue.

Specific to my current TPS issue, does anyone know if the Innova 5310 will capture TPS and MAF data? I called their customer service and they did confirm the 1998 XK8 was supported and will do some data streaming. They just couldn't tell me if that included TPS monitoring. Answer was "it depends on what the manufacturer allows".

 

I just used my ACTRON CP9180 that I bought more than a decade ago for generic use.
It reads the TPS and MAF on my 1998 XK8.
I have not found a car with OBDII (1996>) that it will not read data.

WDS and IDS will communicate with all the modules but if you just want the ECM, most any 'scanner' that does DATA will work.

P.S.
ALL AJ26 throttles will work. (XK8 and XJ8 all the same)

 

There is a DATA READ for the 1999> Normally Aspirated and 2000> SuperCharged (AJ27) called THROTTLE DATA--DOWNLOAD CAPTURE where you can read a 2 character code to see if the throttle malfunctioned and stalled the engine.

I don't remember if it is an AJ26 function but I remember using it for faulty throttles when I worked at the dealer decades ago.

WDS or IDS is required to read the data. I don't know if other diagnostic devises will work.

 

Good info, good to know. Thanks for your help and advice.

 

Good info, good to know. Thanks for your help and advice.

 

Yes, I've heard that claim before, but the reality is only the standard PIDs have native support in apps like Torque. I've never got the extended PIDs to work in Torque or DashCommand.

 

Still no resolution as the Innova unit would connect and read the basic info but failed when asked to data stream. Harbor Freight tech support says they have one that will work but it is $350 which is above my budget for a scanner. Plus if it doesn't read data streams there is a 20% restocking fee to return it. Gave up for this weekend and will start again next week.

side note: I did a hard reset for another task and the acceleration issue seems to be improved. I guess all my driving in crowded North Dallas traffic got it's brain used to slow takeoffs and quick shifts well below redline. Will try to do better with that performance aspect going forward (within legal parameters of course).