I've had this problem intermittently for 5 years now. It is always associated with use of cruise control. The dealer checked it various times but no code was ever stored. It actually resets itself most of the time, if you turn the car off and restart.

More recently, while idling (either cold or warm) stalls and fails to start. If you keep cranking you notice free (lack of compression style) cranking. If you let it sit for a while and remove the fuel injection pump fuse while restarting, it will clear up and start momentarily. Repositioning the fuse and restarting has done the trick for me. I suspect that the fuel injectors remain open and flood the cylinders washing lubrication and loosing compression while you keep on cranking.

Also, failure to start your 4.0L engine for more then 2 weeks can cause it to loose hydraulic pressure, thus compression and again flooding your cylinders with gasoline, etc. It has happened to me on both my 1998 XJ8 and my wife's 2000 S-Type. The dealer ripped me off by charging $85 per spark plug plus labor allegedly because the plugs were fouled by the flooding with gasoline. All under original and extended warranty periods. Again, by removing the fuel injection pump while restarting will do the trick.