The secondary air intake pump is there simply to feed the exhaust sys air and
get the cat converter up to temp quickly (liking blowing on a campfire to get it going).. this reduces emmisions as the cat is hot shortly after start up.
If the air pump dies it is not a driveability issue. However, if you have to do the smog check in your area your car will not pass as the check engine light will be on. I replace the air pump on my 98 jetta.. not only was it a PITA to get to it cost $400.00.
I got it in just before my tags expired and then the CIL came on again. Seems a associated valve was faulty also ( the pump on this car was FULL of water and that
is probably what killed the check valve..) Anyway this was the last day on my tags so I had to do something.. I cleared the codes.. unhooked the battery an then hooked it back up.. clearing anything in the computer's memory.. and drove straight to the emmisions station. As I had cleared the memory they had to go back to the old way of sniffing the tail pipe emmisions instead of useing the car's OBD II diagnostics port.It passed.. I got my tags..:-)
The only good thing here is that the air pump on the s-70 is pretty easy to get
to as it is in the wheel well as i remember and not under the intake manifold as it is on my Jetta.
If yours is making noise it may just need the drain hole drilled to get the
water out.. or it could be the check valve is acting up which is the cheapest fix!

Good luck and dont worry about driving the car under this condition..
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vw bus site w/ Volvo section - http://www.geocities.com/vw_bus_74/index.html