Hi db,
My daughter's car is the same year and model as yours. I bought hers with a bad air pump which got me an excellent deal from a dealer that did not want to deal with the check engine light. Following is the procedure to r & r the air pump:

http://volvospeed.com/Repair/airpump1.php


I did the vw air pump conversion that got the problem fixed cheaply with a like brand new pump from ebay for like $60 shipped. Here is the procedure to convert:

http://www.matthewsvolvosite.com/air_pump_replacement_850.php

An additional note: in the writeup for r & r it is suggested to change the sas valve(mushroom looking gizmo) . I picked up 1 from a junker because it looked fairly new(and I was too cheap to buy new). As it turned out this didn't seal well at first(found this out by spraying PB into the hose openings and saw it leak out through the base). This thing gets gunked up like an EGR valve can because of exhaust passing by sealing end. I just let the PB work it's way into the valve and worked it by applying vacuum several times. Result was a valve returned to a functioning unit once again( as proven by no PB leaking out through the base). I bet the original can be brought back this way too and will try it when I have spare time. As an added measure I also drilled a small hole in the pump housing in case(when) the valve stops sealing again. Overall a very easy procedure and the S70 has been fine since August 08.

Hope this helps,

Dan