No matter what the map the minimum boost should be wastegate spring pressure. The fact that you had boost the previous day and now you have near zero probably eliminates a mechanical failure of the turbo. Do you still have the whirring noise from the turbo?. Going back to the Diverter valve I assume the solenoid is powered to close and not powered to open?.
Looking at Boomba racings "boost operated blow off valve" seems to confirm this. Are you getting any voltage signal at the diverter valve?.
http://www.fiestastforum.com/forum/threads/10114-Boost-Operated-Blow-Off-Valve-Boomba-Racing
Looking at Boomba racings "boost operated blow off valve" seems to confirm this. Are you getting any voltage signal at the diverter valve?.
http://www.fiestastforum.com/forum/threads/10114-Boost-Operated-Blow-Off-Valve-Boomba-Racing