well I had a problem with my mk2 a couple months ago. when started from cold it would idle fine for as long as I wanted. but as soon as I hit the throttle it would misfire and cut out. then wouldn't start again for about 15 mins. turned out the pressure relief valve in the oil pump was stuck. was fine at idle when the pump was turning slowly but as soon as it was revved the oil pressure would shoot up and overpressurise the hydraulic lifters and keeping the valves open. so I would get an oil pressure test just to be sure. it may not be your issue but there is a chance.