The early TDI's have the MAP/pressure sensor inside the ECU, on the circuit board. (as opposed to on or around the intercooler on later models)

You have to disconnect the battery, and leaving the ECU harness connected, undo the 4 small torx screws and open up the metal ECU body.

Inside you will see the small black rectangular 'circuit board' mounted MAP sensor, which is connected to the nipple on the inner ECU body with a 2 inch bit of thin dodgy tubing.

This is the correct tubing to replace, as it degrades over time, it is held on by 2 small clamps, and is easy to change.