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

:>)

Whats the outside temp? The hesitation is seen in the hot hot summer. I don't think a stuck ABV would have any negative effects in the winter. An easy way to test it is to just remove the hot air duct. If you want to test it, remove it from the air box and use a blow dryer to see if it operates.

Make sure you don't a bad ecu? What year is the car? Are you getting any codes on the computer? Give more description of what goes wrong.

Greetings Carl, I'm afraid I dont have an answer but was curious if your problem and problem I have w/my 740GL is the same...... Ive replaced pretty much same parts as you. My problem is after warming up and then once heading down the road the engine "bogs" under acceleration...let off its ok. If I turn ignition off and then restart (I call it re-booting)it typically runs normal. Ive noticed it also is a bit sluggish at times and other times has the normal "pep" i'm used to. Where is the airbox valve.... how much was it and whats the IPD catalog? Sorry to ride your tail of your post but I'm getting ready to head out on road for work and like to have my old brick in good running order. Thnaks for any input. Fairway