Early FSI and TSI engines had a diverter valve that had an internal rubber diaphragm. The diaphragm design proved to regularly fail even on unmodified cars. When this fails, you will see a large drop in boost pressure and a moderate to severe loss of performance.
VW/Audi replaced the diapragm valve with the "D" revision that has a composite piston instead of the
rubber diaphram. This piston style revision has proven to be far more durable than the original design.
*If the number on your original diverter valve is 06F 145 710G you have
a diapragm type and can upgrade to this piston style.