My 2003 XK8 Engine 4.0L AJ27 went in to limp mode a couple of times. restarted the car and it drives fine for a while. I checked the codes and P0121 = TPS 1 and 2.
I removed the throttle body and took it to ASI (Automotive scientific Inc.)
They are located in Rogersville, TN. phone#423-921-9085.
Put the throttle body back and have been driving the car for a week and it drives like a charm again. I was lucky I did not have to adjust the idle speed and sometimes that is necessary. I marked the position of the TPS, and when I got it back it was in the same position.
I just wanted people to know I paid $239.00 for this and it beats buying a new one. I dropped it of and picked it up because I live 1 hour from Rogersville. They will charge you another $30.00 for the shipping. However it is worth it.
On a side note I changed the octopus cooling water hose when the throttle body was of. I have had a leak for about 2 years and I finally fixed it as well.