On my 91 V12 coupe the throttle cable only pulls the throttle pulley about halfway to the throttle stop. The pedal doesn’t go all the way to the floor either, I’ve lubed linkage in firewall but didn’t help.

 

Can You turn it to full by hand at the tower? Disconnect the rods and see if there's a difference. Stick a screw driver between the rod and throttle tower disk and lift and it will pop off . It you can't get to full throttle by hand with the rods disconnected you have a problem with the tower disk or TPS. If you CAN, it is with the pedal throw, cable or the linkage or throttle blades. Should be pretty easy to isolate the problem.

Could be carpet under the pedal too. Or something under the dash is blocking the upper part of the pedal.

 

Sometimes the throttle pedal itself actually deforms and needs to be bent back.

Also, check the nylon bushings at the throttle pedal pivot point. On my XJS one of the bushing fell out, allowing the pedal to sorta flop over a bit. This resulted in 'lost motion' ....lack of full 'pull'....when the pedal was fully depressed.

Also, the cable is adjustable right at the turntable. Maybe the cable has stretched with age and the adjustment can compensate?

Cheers
DD

 

Very simple fix but back breaking,
Appears that the throttle cable has come loose or stretched at the pedal.
If the wire coming from the pedal slides from the clamp that will happen.
On the throttle body that wire has a 'lug' so no adjustment there.
You need to get under the dash so you can adjust the cable tension/slack.
The fix is to loosen the tiny bolt that holds the cable.
Pull the cable to shorten any slack, then tighten the bolt.
It happened to me once.

 

The tower itself turns freely, the cable just doesn't pull in far enough to open throttle all the way. First picture is at rest, 2nd is as far as pedal/cable will open it. Something in cable/linkage between firewall and pedal must be binding or frozen.

 

Disconnect the cable and find out !

Sometimes the cable itself fails, most commonly if the engine is poorly grounded. If the main engine ground is weak the throttle cable become the ground. Result heat melts the inner nylon sheathing

Cheers
DD

 

I would bet that all you need to do is take the slack out of the cable and tighten up the clamp.

 

On most XJS', there is no adjustment at the pedal end. Both ends of the cable have fixed crimped ends. The only adjustment is the outer sheath at the pedastal.
As was suggested, a bad engine ground strap can cause a ground thru the sheath, melting it to the cable inside. Disconnect the cable end at the pedastal, and see if the pedal moves the cable inside the sheath. If not, get a new cable, and add a ground strap between the engine and chassis.

 

I am pretty sure that the throttle cable linkage on a LHD pre-facelift v12 is in two sections. The cable does not go all the way to the pedal, but to a linkage. From the pedal to the end of the cable there is a linkage system. You have to remove a panel (from memory) on the engine side of the bulkhead to get at this linkage.
https://parts.jaguarlandroverclassic.../brand/jaguar/

 

found problem, cable is shot, shield melted, going to need to find one.

 

If the shield is melted, the engine was probably using it as a ground path because one of the ground straps is dirty or broken at the connections. Fix the grounds, or you're likely to fry another cable