During driving, though after a few times of it happening I realised it was never whilst actually moving, but when stationary (eg: at roundabout/T junction), I'd move from P or N, into D. It may have happened differently a couple of times, too, say, off the accelerator, come to a stop, foot on brake, look down - engine's died.. but difficult to remember precisely.
There seems to be a 'sweet spot' when it happens - not
immediately the car's satrted- because the idle is still high, not when the cars nicely warmed up over 90
oC, but in between - idle has dropped to 500rpm, but the car's temp isn't up to normal operating temp yet.
Perhaps this is also related to, say, a drained battery which isn't having much charge put in it as fast as it could, so after those few mins the car's took out more than it's put in - after those few mins then the slow-to work alternator has finally brought the battery back up to a decent voltage... again, just a theory
idle control valve is a two min job to look at and check its operation, will add that to the list for tomorrow.
stop screw for the TPS? Haven't noticed it recently, but last time I did it was in the correct place - but will check this. Has never been fettled with - still has the little blob of yellow paint on the screw/nut done by Opel in the factory.
edit: Just to reiterate if I've not made it clear - we're not talking of a shakey idle which then shudders, and the engine dies - we're talking about a smooth idle - often the first I know of the engine cutting out is when I put my foot to the loud pedal and realise the revs are at 0. It just cuts out instantly, like the DISpack/ECU just loses all power(?)