The electromagnetic clutch on the air pump is only activated during initial start-up, and remains engaged until a certain temp at which point it disengages.. I believe the pump draws it's air through the long hose which runs up to the cleaner body, with a small air filter (1.5"x4") on the inside of the cleaner. If you have no air pump, and no plans on re-installing one, then you need to close off that gaping hole. No sense subjecting the main air filter to excess amounts of road dirt/dust.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.