Hi folks!
this is my first post, so hello to you all out there.
I've just had the fuel pressure rail changed on my 55reg td4. It has solved the problem of her cutting out whilst idling. But it now wont start properly and feels very sluggish. Also when she gets around 2000rpm i get a hissing noise like the sound of high pressure steam escaping. I had none of this until i had the sensor changed. Any help would be appreciated before i waste any more money

I think you have 2 separate issues,the steam escaping and lack of power is most likely a loose or split turbo/intercooler hose.The poor starting is usually low fuel pressure due to failing electric pumps or excessive leakage within the injectors.There are other causes,but the 2 I mention are the most common.
A diagnostic session is the best way to sort this out by somone who knows what values should be present at cranking,then a leak off test if the low side fuel pressure is Ok.