Jerry,
   Usually when these cars act squirrelly on start-up likes yours, they are
in need of a CPS (Crankshaft Position Sensor).  What this sensor does is
read the timing of the crank shaft in order to fire the spark plugs in the
proper order as well as the proper timing. When the one on my '88 XJ40 went
out, the car stalled at an intersection, started,  ran and stalled again.
The last time it did it before I replaced the sensor, the car ran
beautifully, died, sat for a half hour, started and ran again with out an
apparent problem.  Once I replaced it, I have gone 20,000 miles with no
stalling or ignition problems.
   If you have checked that you are getting fuel to the rail and spark to
the plugs, chances are this is your problem.  It is about a $60USD solution
and you should carry a spare in the trunk.  Also make sure that the one you
get is for the 4.0 litre engine and not the 3.6 if your car is 12 years old.
They do not swap.
   By the way, my 1960s Jag is an old Jag -- your 12 year old Jag isn't
even broken in yet.  I have 210,000+ miles on my '88 XJ40 and I plan to take
it 300,000 to 350,000 miles before I do a re-build on it

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