Hi RobJP, thank you so much for taking the time to reply to my problem but alas it has had a new fuel filter fitted and Im sorry to say that there isnt a fuel filter heater. thanks again anyway..

If worn damaged turbo vanes, why is it ok above 3 degrees? and any fuel starvation would give a low rail pressure fault code.

When you say its only bellow 3 degrees, do you mean an over night stand or when ever the outside temp reads 3 or below it happens while driving (ie driving fine at 5 degrees but 10miles down road it gets colder and below 3 fault suddenly occurs)?

Does the Under Boost fault code appear everytime when the vehicle loses power, and if you stop and restart the engine is the power restored? (Once under boost detected engine will run in limited power stratagy until restart, even though reason for fault may have disappeared)

First thought would be (as you have said the soloniod changed that its vaccum operated) the vacuum hose from soloniod to turbo actuator may have water build up and freezing at low temp and therfore no vacuum able to pull vanes into position. however there is other possible causes, any further info you can give might narrow it down a bit

Hi, no this is the 2 litre..many thanks

Lots of new parts but no mention of the one part that alters with temperature,

And that would be the Coolant Temperature Sensor.

That would show up on live data of course. If the engine temperature reading on the scantool said 40 degrees, and the actual coolant temperature was 5 degrees then we could suspect the sensor was bad. The point is it's easy to check.

Thank you hardway, I will mention this to the garage tomorrow.