To me it looks like a Pierburg dashpot (see the photo), but which one is the big question. I get the impression they come in many damper configurations. It's probably not even critical, It's only to keep the deceleration manifold vacuum from spiking on closed throttle and to let the throttle down softly. High vacuum spikes cause incomplete combustion in the cylinder and therefore backfires in the exhaust system (and bad emissions, for you tree huggers).
The one in the photo is for an old Saab and the part number is W01331619541APG. It pops up everywhere on the internet if you search that number. I wish I knew more about it.
Tom Kizer