[chittychittybangbang]

First, the routing for the blow off valve could be faulty and the vacuum lines causing the malfunctions. A blow off valve won't do anything because there's no throttle plate for it to act against.

Yes it sounds like you're losing pressure on the turbo but there are many possible causes. It's possible the MAF sensor isn't working properly - read the link and do the tests. The only way to know for sure is to do the tests yourself...or pay a mechanic to. There are other causes like a boost leak or leaking vacuum lines but you have to test for them. They are listed in the link.

What strange noises do you hear with the engine running? Idle only or while driving? Please be specific. I don't think it effects the tubo pressure.

 

[chittychittybangbang]

i recently replaced my clutch and pressure plate as well as flywheel, since then the turbo does not work at all. Could the clutch and pressure plate replacement be the cause of this? if not, then any suggestions on what it could be?

Is it the same AHF engine? If not it should be in its own thread so it doesn't get confusing in here.

The clutch and PP replacement will not cause that problem, I am sure. However, the vacuum lines to the turbo could have been disturbed or a sensor could have been unplugged which causes your low power situation. Take a look at the low power FAQ here and work through the list. http://www.myturbodiesel.com/1000q/multi/low-power-fix-TDI.htm If you're stuck anywhere or need more help, please post what you have done so far.