Take off the air filter housing and you should be able to look down and see the butterfly valve. It's sort of an electro mechanical device controlled by the engine management system based on inputs from various sensors and systems in the car. You might get some insight at siemensVDO.com. They refer to them as engine actuators. As I recall you can download a product catalog that has at least some basic information on how they work. Cleaning the whole thing up is the easiest, cheapest thing you can do. There is a place on their web site that says that replacement parts are available to rebuild them but I looked high and low and could not find them in the U.S. I think MB USA likes selling the replacement units.