I saw this on another Jag site and the thread was discussing a progressing interference between the throttle linkage and the frame. I also had this happen recently and it seems to be common. The fix it to rise up the motor mount on the passenger side with a 1/4" washer, new stronger mounts or a 1/4" shim added to that side mount.
Here is the post:


"My car is a 2+2 auto retro-fitted with a 4.2 intake
and 3xSU carbs. The throttle shaft under the carbs managed
to roll over the frame rail and stick there.
Has anybody else experienced this? Should the shaft (and
its rods) completely clear the frame rail? Had this
happened while driving, it could have been very nasty.
Incidentally, freeing the jammed shaft/rods was as simple
as pulling up on the intake trumpet to raise the motor a
fraction on the carb side"


Alfred

 

Their is a replacement cable operated throttle for the 6 cylinder xkes, it is made in england as a kit but is very expensive...$400.+
It comes with a new pendulum gas pedal and twin cables it elimiminates all
play and is very smooth and is not effected by chassis flex.

Soooo. I made my own using bike twin cables, a fabricated throttle pedal and adjustable end linkage less than $20. This is a great improvement on xkes for safety as well as a different driving experience. All new cars use this arrangement !