Right here we go... about 700 miles ago I had: new head gasket (preventative maintenance), water pump, cam belt, tensioners, fan switch, water temperature sender, radiator and thermostat. Before the problem started I had just filled up with Shell V Power (never had an issue before). The problem started after about 50 miles. I put a bottle of STP fuel injector cleaner in and the car has been OK... so far. Hopefully thus has cleared it... Good luck Toughie, let us know how you get on.