Air filter
 

I apologize in advance if the answer to this is available somewhere on this forum and I missed it. This is my first visit and first post and am not familiar with the layout of this forum. My question is this, I have a 2007 C280 4Matic and when I changed oil the other day and removed the cover to access the oil filter, I noticed a hose that goes from the front of the air filter to what looks like a pump (although it is not driven by the belt) was not hooked to the air filter. I had it to the dealer for some service 2400 miles ago and they did not hook it back up. What device is the hose hooked to and is there any chance any damage was done by it being off for that long? I am still trying to find out why my fuel milage had dropped from 26 to 24 at best. Through last winter and through this summer I was usually getting right at 26 for what is mostly highway driving. Thanks in advance for any help. I would like to know about the hose before I call the dealer. By the way, my milage dropped before I had it in for service and has not gone up even after I re-connected the hose.