Most expensive sumptom of air box valve failure is failure of the AMM due to a constant diet of pre-heated air.

The air box valve is really a flap that can either cover over the cold air intake, or cover the preheated air intake (silver tube from exhaust manifold area) or be somewhere in between. The flap is controlled by the air box thermostat, a $30 item.

Conspiracy theory holds that Volvo never tells a dealer customer about the $30 part because then they can sell a $450 AMM.

Do what Haroon says and test the thermostat in the air box. Just pull the air filter and blow with the hair dryer. The flap should move towards closing the pre-heat tube inlet.

The theory behind all this, thank you EPA, is that the faster an engine warms up the lesser nasty pollutants it produces.

Good Luck with yours.

Bob

:>)