On my 2003 XK8 the kickdown 'switch' requires very hard pressure on the accelerator pedal to actuate. The black thing under the accelerator pedal is not actually a switch but a spring loaded plunger (The JTIS refers to it as a Kickdown Plunger) with a spring loaded detent sitting on a threaded stud sticking out of the bulkhead. The actual kickdown function appears to be in the Accelerator Pedal Position (APP) sensor at the other end of the cable, under the hood.

I have tried removing and lubricating the plunger but that has not helped. Has anyone else noticed how hard it is to depress the plunger and discovered a fix. The plunger looks so simple that I doubt a replacement would help.

I suspect that the earlier cars with the 4.0L engine and 5-speed tranny do not have the same system. I tried looking in the JTIS for earlier cars but came up empty handed (No surprise!!!!)

 

Can't help on a fix other than screw it on as far as possible, the 4.0ltr has the same thing but the difference being it is actually a switch and gives you a double kick down when depressed unlike the 4.2 6 speed box.

One reason why I prefer the 5 speed tranny

 

My 'kick down' was but all inoperative until I took the slack out of the throttle cable at the TB. Now, just punch it and it kicks right in. So you might want to look to see if you have a little bit of cable stretch at the TB...

Only thing that I do not quite understand about the 'kick down' beneath the gas pedal, is the little bit of turn (1/4 to 1/2 turn between stops) that is there and if it means anything or is some sort of an adjustment???

 

I found this switch in the glovebox. From what I find it is the kickdown switch or part of it. Is there something missing? Is is supposed to have connectors? If so there are no wires lying about by the the accelerator pedal. Very confusing