A friend of mine is a master volvo mechanic and he gave me that advice. I haven't been wrong by him yet. I don't quite understand the problem either, since the exhaust manifold is pressuized by the exhaust and forces the air out into the air pump when the pump fails. On the other hand, the air pump is providing air into the system through the valve, so it must be able to overcome the pressure of the exhaust manifold to be able to force air into the manifold during cold start conditions. My guess is that there is no "pressure" from the manifold at that point. Most of the air pumps fail due to the moisture from exhaust condensation getting into them and flooding the rotor. If the exhaust was acutally getting into the air pump with any pressure, the water would not have a chance to condense in the tubing or air pump.