Usual cause of this is the high pressure pump. As the pump wears out it actually over-fuels. If the van is fine when under load (accelerating up a long hill for example), but only causes a problem when you back off, then that's the HP pump on it's way out. So far I've not found a specialist who can repair these pumps cheaper than the cost of a new pump (about £350 from the dealers).
cieranc
May 2013
howtomendit.com for free repair help, information and advice.
