Hi everyone, have had this same issue on going for the last couple of years, I have a 2003 XKR and each time I drive the car I have this fluctuating Rev issue, it happens between the 1 - 2 thousand rev counter reading and while a slight load is on the car, a small incline for instance.
The car is with a mechanic a the moment and he has no clue what could be causing it.
After the car is fully warmed through the problem seems to disappear until the next day when the whole process will start again.
Just wondered if this rings a bell with anyone.

Cheers Moosey.

 

It is the torque converter clutch locking and unlocking. The variation is a couple hundred rpm and it’s caused by a known issue with the design of a seal in the early 6hp26 transmissions.

Mine has had the issue for years too and I just baby it when cold. Some day I will rebuild the trans and torque converter.

 

Thanks very much for your input, I will let the workshop know.

 

Mine does this as well. It's around 40mph when it happens. I only noticed because it felt like the car was accelerating and decellerating slightly, I looked at the rpm and it was increasing and decreasing by maybe 50-100rpm. Is it a bad sign?

 

It would not hurt to do the following:

• Fluid/pan/filter change with Mercon SP, and do the connector sleeve, bridge seal and tube seals too while you are there.
• Re-flash the transmission control module with the "latest" code (SDD)
• Run the re-set of the transmission adaptations (SDD or JLR scan code)
• Check tire pressure on the rear to be sure it is correct and the same left/right
• Check the condition of the rear wheel bearings
• Check the engine fuel trims with an OBDII tool in the same Load/RPM zone as where you are experiencing the problem. Make sure the long term trims are as close to zero as practical, or, say , < 5%

Best of luck, keep us posted.

 

Thanks for the advice.