1991 jaguar XJ6 4.0L Stalls

SOURCE: Engine starts but cuts out as it settles to idle revs

is the check engine light on ? find dle air valve mounted on throttle body ,remove an clean with spray carb cleaner , or look for vacum leak.

SOURCE: jaguar xj6 1991 2.9 manual

2 things, first of all teh distributor cap and rotor go bad causing the car to have spark but not fire, secondly you need to make sure that you are getting fuel to the engine bay, if not then it could be the fuel pump.

In regard to the other gentlemans question, starts but cuts out I would start with the same process and open your fuel flap and make sure there is no water around the filler area as it sounds like you could also have water in your gas. (there is a drain next to the filler neck and it gets clogged over time, then when it rains or you wash your wash, that area fills with water and seeps into the tank)
JPTCAT

SOURCE: 2001 Jag S-Type stalls at idle

whats the fuel pressur like last time the fuel filter was changed and is there flow at the ehasut

SOURCE: Jaguar 1995 XJ6 idle doesn't hold

I had this problem with my wifes car. I went through the car top to toe and found more than one problem causing this intermittant issue.
I found a weak crank sensor, when warm it was intermittantly losing a signal, replaced it and the problem was a little better, I then found that the throttle position sensor was also intermittantly not within the range it should be, replaced it and it helped, I then was getting the oxygen sensor code and that was only due to the car stalling, nothing to do with the o2's, I finally traced the final issue to the integral harness on the valve body inside the transmission, I replaced that harness and fitted a new transmission speed sensor and the car has been perfect.
I know you have several issues here that could be your problem but you now have a base to start from.
Last thing is the car may just need an engine set-up if you are no longer having any codes. This is only done by the dealer using there WDS computer system. The perform a oxygen sensor orientation test, they set-up the kick down and also set-up the Throttle positon sensor (TPS).
Hope this helps.
JPTCAT