2000 XJ wont idle???Please help

I have had so much help from you guys and just when I thought I knew it all I am stumped. My mother in laws 2000 XJ 4x4 4.0 auto just started idling at 500 rpm or below and frequently dies??Starts right back up and runs great until at idle? Any suggestions. I was hoping for bad gas but I am thinking fuel filter or fuel pump time? Help from previous experience would be great.

First thing to suspect with symptoms such as yours is the idle air control. Located on the throttle body; two screws gets it out. Remove it and clean it and the seating area with throttle body cleaner. Clean the throttle body itself as long as you're in the area. Re-install idle air control. See if that straightens out your idle.....

ok, put new plugs in and cleaned the throttle body and the IAC. Seems to be running good, we will see tommorrow. Thanks for the advice I didnt feel like changing the fuel pump