You made me do it. I had to go out into the garage and look at my 1995 940. I have the same disk but it has a purple wire coming out of it. It is in a larger hose that is connected to the Air Filter box. My hunch is that it houses a sensor - probably a pressure or flow meter type of sensor to detect airflow in the larger tube. My hunch also is that it is a pollution control allowing air to recirculate or to vent into the cumbustion air intake and the "disc" is a sensor for flow. If you're running OK - leave it. I do have a half decent shop manual and can look it up but I cannot guarantee that this shop manual will properly ID it.