head gasket failure is mostly linked with overheating and increased pressure in the cooling system and is vented through and out of your expansion bottle(where you top up) it is also possible for the head gasket to fail between two cylinders,this allows water into the cylinder and on combustion white smoke is visible at the exhaust,this white smoke will be visible from idle most likely get worse when engine is under load.going on your description I don't think this is the fault and neither is your fuel filter .I think there is a sensor on the intake manifold that has something to do with the turbo ,not sure , but I think the fault is turbo related.if you don't get much luck on here try a reneult forum ,someone on there should be able to help.
tm
November 2011
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