I have a 1998 XJR which has recently developed an intermittent fault where
it will some days have power drops under very light acceleration.
Accelerate hard and it goes fine.  Sometimes the effect is very bad and you
wonder if the car is going to stall out (it never has though), and it will
just jerk along till you accelerate harder.

I have repeatedly had the car back at the jag main dealer - and they have so
far replaced the n/s wiring loom, and most recently the air flow meter, but
so far no improvement.

The car has had a new engine about a 18 months ago and a new throttle body
before that.  It has also had an Romano sequential LPG conversion 8 months
ago, but the problem occurs with either fuel and also with the lpg system
disabled

If anyone has any ideas that might save my sanity..