Arr, the old playing up when warm habit. Two MK3 16vers and one VR6 I know of have recently been cured of similar problems by changing the ECU supply relay. It lives in relay position 3. 3rd in from the left on the second row up from the fuses. The number printed on the relay changes depending on ECU. A tenner or so new from VW but also worth popping the case off and having a look at the state of the contacts. IIRC, the coil from my 16ver is significantly smaller, so if it's the same size the odds are good. If it's still readable I'll get the VR6 Dizzy coil part number from mine later j