Weak boost.

[gingejrmorgan@me.com]

10th owner on an 07 GTi. Had a remap which I was told that it was overwriting a previous sh*t map. Was happy as Larry. The thing was a monster. It’s just hit 100k and recently started hissing at the power band and doesn’t vent when I let off the pedal. It no longer has the naughty attack when it hits the band. The boost is 25% of its best form. I’ve had several garages look at it. All said there is no leak and the turbo is running fine. They just can’t pinpoint the issue. Most recent said it could be the solonoid (turbo sensor) has anyone had something similar? I’ll be honest. I rag the pants off the poor girl.

[bacillus]

torn dv diaphragm ?

[Clarkj93]

Sounds like you may need a new diverter valve. It's a well known failing point on these cars and not that expensive either.

[ROH ECHT]

Is a diverter valve the same as a dump valve?

...same as, in VW terms, "Turbocharger air recirculation valve N249." The DV (or any of the other terms used for it) contains boost until commanded to release it back into the turbo inlet.
Here is a saveable/downloadable PDF;
http://www.volkspage.net/technik/ssp/ssp/SSP_337.pdf

The hissing and lack of boost is likely the DV. As it is probably the more common fault for this. But it may also be a large air inlet leak or a damaged PCV. You can quickly test the PCV, just to rule it out, and its capability to contain boost by disconnecting this tube at the arrow and blowing forcefully into it. It should be sealed;