Scot - Something just occured to me. Old Hondas used to have a similar problem because there was an O ring around the map sensor that would go bad and boost would leak past it. Something else to look at.
I might have to take it into the volvo dealer - but I HATE doing that. It costs an arm and a leg! and sometimes they cant even figure it out. What makes it worse is that its in SLC!!! (40 min from here)