Hi, new to forum. Just picked up a 96 Vanden Plas with 238,000. It sat for a year, drove it on Sunday, throttle hesitates to return to start position when foot removed from pedal. Car tends to "get away" from you over 50mph. It will eventually return. When stopped, engine off, hood open, the throttle cam on the throttle body will return as normal when manipulated by hand. Any quick and easy solution to this condition? Thanks very much.

 

There was actually a technical bulletin issued regarding the throttle spring problem.
You could disassemble the throttle and adjust the spring with pliers.
Here you can see the procedure which I did.

ƒWƒƒƒK[X300^XJS@ƒƒ“ƒeî•ñ•ƒp[ƒc”Ì”„@`ƒXƒƒbƒgƒ‹‚΂˒²®`

You may also need to clean up the throttle butterfly. It often gets sticky with blow by gas.

 

Welcome to the forum. Here's another:
https://www.jaguarforums.com/forum/xj-x300-xjr-26/no-cost-solution-sticky-throttle-return-spring%3B-h-t-motorcarman-111454/