After reading the facts sheet on the TT I think the boost problems and hissing noises are due to a broken diverter valve. It makes perfect sense considering there are no other hoses that are damaged.

I'm a little un-clear on the testing procedure for a DV failure. Do I remove the vaccume hose on the top of the DV? I'm not sure what to do to test, the directions of the fact sheet didn't make perfect sense.

 

testing for a split DV diaphram?

Take it out, push a capped pen up into it from the underside, and then cap the vacuum barb with your finger and release the pen. DV should stay open until you take your finger off the barb. If it falls as soon as you release pressure with the pen, its obviously split, and bad.

 

Simple enough. I just drove the car and there is definitely adecline of power but the turbo is still going. This definitely sounds like the problem.Would this malfunction also be causing the hissing noise, or is that still a boost hose out somewhere? I can't seem to find a bad hose.

Thanks for the help

 

Well, if the DV is torn, boost pressure is being cycled back around to the unpressurized side of the turbo. You want that when you lift off the throttle (the reason for the DV is making a place for boost pressure to go when it cant get past the throttlebody), but obviously not when you're trying to make boost. It'll kinda be like the 'whoosh' noise of a BOV, but all the time you're on the gas.