If I stop while on a journey (say to pop to a cash point) for a short period of less than 5 minutes the car will start but not rev to enable the car to be driven. If left for a longer period 7 or 8 minutes it works as normal. also happens when cold, if I move the car off the drive, go back inside to do something and the car will not rev unless left longer between restarting. Can anyone throw any light on what the problem may be?