My 99 XJR has been sitting for about 6 months. Yesterday I replaced the battery, and I bled and replaced the fuel. I used some primer to get the engine started again. It will start, without the primer but will run for only about 30 seconds and the RPMs drop and the engine cuts out. Application of the accelerator cuts the engine immediatly. The oil needs to be changed too. What would cause this? Would re-setting the computer do anything? Is there a way to get the new fuel circulated in the engine? There is a clicking sound in the trunk when the key is turned, I believe this signifies the fuel pump is working.

 

Get a fuel pressure reading at the fuel rail first. Should be 42lbs +/- a few.

 

SHould hear more of a short 'whirrrr' than a click... possible siezed fuel pump? There are two in the XJR, but it's very common for one to fail without the user knowing it, and then when the second one goes - poof - no run.

 

When you replaced the battery, you may have affected the memory in the ECM that controls the idle speed. It happened to me a few months ago. Start the car and use the throttle to maintain idle. After a few starts, the ECM should re-memorize the idle setting.

Sorry, I wrote this before reading your complete post. If you can't control the idle with the accelerator, then the problems mentioned above are more likely the source of your problem.