No start on the old 96er, with clues

My '96 XJ has been my daily driver for years/decades now and she's got 220k miles behind her. My Mom's car needed some work so I traded cars with her while I get hers done. She doesn't drive nearly as much so it's only been started once every week for about the last month. On Tuesday of this past week Mom leaves the key in the ignition and turned forward to the on position so she can close the windows. Well, she forgets to take the key out so it stayed in that forward position until yesterday when she went to start and it was totally dead. Yesterday she and a neighbor jumped it 3-4 times, the engine starting each time with a little gas pedal then it stops.

So I get on scene today and charge the battery up real good, and crank to start without giving any gas pedal and it doesn't start. So I charge again and try to start WITH a little gas pedal and it starts right up, but you have to keep the RPMs up to keep the engine going. After starting I let the engine run at about 1500 rpm for about a minute, and as soon as I let off the gas the engine goes back down to idle and dies immediately.

So at least we know the engine runs, which cuts out a lot of guess work. Now I need to figure out why it won't stay running.

Any ideas? What should I check?


PS. All fuses are good and the fuel filter is only a year old.

I think I'd start with the fuel filter ..... if nothing else to cross it off the list.
Does your XJ have an ODBII port? If so, you may try to pull some codes and see if it will tell you what's up.

Mark makes a good point, it could also be the fuel filter / bad gas.
Clean TB and IAC. Your IAC controls air during idle. Check wiring and connection to the IAC as well.

Never look down on anyone unless you are helping them up - Jesse Jackson

swap in another battery to also test that out. like the one from the car
it could just be the battery is done and killing it