Hi I have a 06 vivaro 2.5 ctd .On long journeys the engine cuts out dead with no fault lights showing. Switch off & then turn the key & it starts up again immediatley. Sometimes I dont even stop but put the clutch in & turn the key and it starts straight away & let the clutch out & carry on. On a journey of 100 mies it does it about 4 times. Local journeys it is perfectly ok.. Any help would be welcome.