There are a multitude of causes for underboost. The likelihood that the turbo itself has failed and is the cause of it, is very remote. It doesn't sound like your mechanic can diagnose and differentiate the various causes so don't trust his "guidance"
What surprised me about the Q7: the windshield rake ends up leaving you with with a tighter entry than I was expecting from a heavy, 3 row SUV. It does ride very nice. You are always aware of its heft and I can see why you'd go through brake pads quickly.
Toby - the turbo is controlled by the vacuum system. If you have a vacuum leak you'll have a) low boost b) shaky shutdown due to inoperable ASV.
For me, the telltale sound I listen for on a vacuum leak is the ASV itself. You should hear the ASV audibly open back up ~2 seconds after the...
Nice. I love a good data log summary :)
300k miles logged on mine over ~410 fuel ups since Feb 2006 (didn't log many miles in 2020, 2021). Interesting the miles/tank average. 730mi/tank vs 470mi/tank. I admittedly go well past the low fuel light EVERY tank .