I found another problem under the hood of my 1998 S70 GLT. Just About to install my Boost gauge and noticed two hoses that are both vacuum lines where disconnected. I have a diagram but cannot figure out where they go one is the red and other is the blue. I will take pictures of the valve and hoses tomorrow. And as one explained in the link below they get the boost cut from an over boosting turbo which i have been experiencing for a while but till now couldn't explain it.
http://www.matthewsvolvosite.com/ima...iagram-850.jpg

 

The red line in your diagram should go to a manifold port, usually close to the throttle body. This is the CBV and is independent of boost controller.
The green line senses boost at the turbine outlet, whish is sent to the electronic boost controller, which then decides how much boost to cut or add and controls the wastegate by using the yellow line. The blue line I am unsure of, it is probably either a reference line Senses absolute manifold pressure) or an actuation supply line (again, manifold pressure or vacuum)