JAGUAR XJ8 Sport - X308 Cutting Out

Q
I am experiencing a problem with my 1997 XJ8 3.2 Sport that is rather frightening, as on four occasions in the past four weeks the engine has cut out without warning, once on the A1 at 65mph. There are no warning lights other than an eventual message saying engine stalled or engine failed, and once turned off the engine always starts straight away, albeit sometimes with a puff of smoke.
I also have a problem with the airbag light coming on - after a wiggle of the wires under the driver's seat or the putting of weight on the passenger seat back it then goes off for a few days.

A
A build-up of carbon within the throttle body can cause the butterfly to jam shut on deceleration, starving the engine of air and causing a stall. Once the engine vacuum dissipate the butterfly can then open again under spring tension and the car will start as though nothing as happened. This situation is more likely to occur if the part load breather is also blocked.
With regard to the warning light, we would recommend a clean up of all plug contacts and a thorough check for trapped or damaged wiring, not uncommon in a seat harness.