Searched the forum but didnt find anything,dont remember my 98 XK8 having it and the 2001 XKR doesnt have it.
Just a big black knob under accelerator you can screw up and down to limit throw of pedal?

 

It's a kick down switch but on the newer cars they got rid of the function. I removed mine because it doesn't do anything on the 2003 cars and then adjusted the throttle cable so it's correct. Only good thing you can really use it for is if other people drive the car you can limit the throttle so you can't get 100% out of it.

 

Thanks!
Guess it doesnt do anything on the 1998 either,,I removed it and the transmission kicks down just fine and the car feels peppier on the highway, guess the it was keeping throttle from opening all the way,,not its just a bit slow not a lot slow,LOL..

 

I think that this has been covered a few times before.
Upon ever reconnecting the battery for years and years, I have always reset the throttle body and accelerator range by turning on the key without starting the engine, then slowly depressing the accelerator pedal till I feel contact with that pedal switch, and then continuing to depress the pedal to the floor .Finally I let the pedal up slowly. I do this again a second time, and then start the engine. I do not think that it has anything to do with my kickdown, but much to do about the reset.
It has been second nature to me, Can anyone back me up or else enlighten me?