If you didn't touch anything else then a boost leak would be the obvious suspect. If your car is anything like mine ('04 Seat Leon with 1.9 TDI engine) then VAG use metal-ended pressure hoses with two protruding lugs on the male end which are located by a metal spring clip on the female end of the joint. These joints are prone to wear of the lugs and eventually stop sealing. Perhaps you could re-check the joints to see if there is any noticeable gap between the metal flange end of the hose and the mating surface of the joint - there shouldn't be.

Also, the sealing rings in the joints were modified from a black, circular O-ring type to a green, square design to improve the seal. You may have damaged or disturbed the seal when you put the joints back together. It's best to lubricate the joints with a little engine oil when re-assembling to lubricate the seal as it's pushed back into the joint.

The newer seals work better so might be worth changing them if you have the old type. Apparently main dealers don't sell them separately to the hoses themselves, but I've managed to buy them from SERE Motors in Northern Ireland via the Seatcupra.net forum.

HTH.

Either one of the joints, and there must be eight has not gone together properly and is leaking or you have caught a vacuum pipe and pulled it off. Maybe you caught the Turbo actuator vacuum pipe. Regards Peter

Many thanks for all the responses.

Upon investigation I noticed that one of the pipes was not fully pushed in, stupid me.

Feel foolish now but just panicked when 'turbo' = ££££ involved.

MAK