Hi all:

1999 XK8. Today, DTC scan showed P0121. Symptoms: ignition on, engine not started, can hear TSP clicking for far longer than normal as it tries to calibrate. Engine on: very high initial RPM, approximately 4000. After a few moments, RPMs settle down to normal. Foot off pedal, place car in drive, RMPs increase to 1200, car slowly accelerates on it own.

Replaced throttle body approximately 2 months ago with a brand new out of the box Jaguar dealer sourced throttle body. Driven approximately 300 miles since replacement. Car operated completely normally until today.

Assuming the new unit is good, what else besides the throttle body itself may cause this issue? How can one test for these other possible causes.

Thanks for any help you can offer.

Thom

 

There was an issue with the wiring harness connectors on your model year that is worth looking in to as you have already changed the throttle body:-

http://jagrepair.com/images/TSB/XJ/303-58.pdf