Does it happily restart afterwards
or do you have to wait 5 - 10 mins for it to restart?
If it happily restarts, i'd suggest cleaning the throttle butterfly valve, when they get gummed up, the throttle shuts, and the crap closes the "idle" gap completly and engine shuts off
This can be done easily with a wrag with a little WD sprayed on and a quick wipe
you'd be surprised what will come off
Ensure engine is off tho before doing work
Also check the mk2 / mk2b guides section, im sure there was a decent guide in there too
Ziggy