My 2000 XJR went into restricted performance mode and had a pending p1121 code. My first response was a bunch of expletives I cant use here. I figured a Theottlebody was in my future.

I decided I would look around. It appeared my TPS connector was not fully locked . Disconnected connector and look at TPS pins with a mirror. Behold i find corrosion on pins. Cleaned terms with terminal tweezers and contact cleaner. Behold, no more issues.

What made me suspect was that it happened in very high humidity/rain situation on cold starts.

Look before you leap....(no pun intended)

 

It's also caused by the pins on one plug being gold, and the other plug being tin, so they corrode because of the different metals.
If the clips on your TPS are broken, like mine were, a cable tie around the whole assembly makes it nice and secure, and I've had 3 months of trouble free motoring since.

 

And use a little bulb grease

This tip form some other board member worked for me.