My 05 XJR has 74k miles, bought it about a month ago,
I have been extremely pleased with the vehicle overall. I am going through some of the basic maintenance items.

One symptom ive noticed is during warmup, at lower speeds (35-55mph) the rpms fluctuate. It feels like the torque converter locking/unlocking. Other times if i look at the rpm gauge, i will see it fluctuate about 100-200 rpm or so.
Should i be concerned about this? None of these symptoms exist once its properly warmed up.

I do have all parts necessary to do a transmission flush, including ZF LG6. I really wasnt sure if the symptoms described above would be caused by older thans fluid or not.

 

I observe the same very occasionally in my V6 with the same trans.

Only semi-warmed up, only at a constant speed of aprox 35 mph in D. When this happens (and that's only like once a month) I just speed up by a few mph or select another gear.

I suspect it's the programming and am not concerned with it. I also refrained from changing the trans fluid. About half of the mechanics I talked to advised to change after 75.000 miles the other half advised not to change.

Since a trans fluid change costs aprox. 10% of the resale value of my car I decided not to change as long as the trans works fine - and it does work fine. Smoothest gearbox I ever had!

 

Sounds like the same issue some S-Types have. People usually live with it I think.

 

Yep living with it , and learning to love the jag querks

 

I've found driving in sport mode it's less noticeable on mine. I've changed fluid 3 times and even tried shudder fix additive and it still does it! So living with it now as it only does it when warming up.

 

I have this problem in the '04 XJ8, and it's been getting progressively worse. Definitely seems to be torque converter related.

I found the following article the other day that mentions, "Sometimes the tachometer needle on the dashboard starts jumping within + - 200 rpm - this indicates the moment of the torque converter lockup failure and the need for repair."

https://kinergo.eu/news/rebuilding-of-6hp-converter-explained.html

These guys are in the business of rebuilding these units, but they make it sound like simply swapping the old torque converter for a new one won't cut it.

 

Common problem...Nothing to worry about...

 

That's because it is the TQ locking/unlocking ! I was told this was an attempt by clever-dick Jaguar software engineers to warm the tranny fluid up quicker so as to reduce fuel consumption. I suppose it saves about one thimblefull !!
I had this on my 2003 X350 and eventually got round it by putting the car into "4" or "3" for a few miles. Once the fluid is warm the hunting stops. My current X350, (actually a 2007 X358 Sovereign) doesn't have the syndrome.I was told you can cure the hunting by changing the torque converter as the lock-up clutch friction plates were reprofiled to eliminate the problem. Personally, I would have thought Jaguar could have just reprogrammed the TCM software and made life easier for us all !!

 

Thanks for the replies guys, Useful information here.
It doesn't seem to cause any driveability issues, so I'll flush the trans out and carry on as normal