lack of power 98 1.9 tdi

[dazg1972]

Hi guys, I'm new to the forum, I have a 3b5 98 passat estate 1.9tdi and have some power issues, the car is fine when I first start driving it but when I rev over 2500 or travel at motorway speeds the car starts to lack power like theirs no boost from the turbo, when I switch the engine off the engine seems to reset itself but then as soon as I try the same as before the same result happens any help would be greatly appreciated so a can enjoy the full experience of my car