What is this called
 

I have a 2003 Ford Expedition, 5.4 engine. I just had some work done under the hood and got the truck back and noticed a line that was hooked to nothing. It ran from something in the passenger side of the engine as far right as you can get behind the battery. I have no idea what this round looking item is called but the hose that is connected to nothing runs from there. The end that is not connected has a black rubber end that looks like it connects to something. I took the cover off top of the engine and noticed right behind the engine up on the firewall, I guess that is what it is called, a black round thing with a tit or point with an opening. So i plugged this loose connector into that. It was the only place I could find that looked like it would take this connector. My truck acted like it was having issues with fuel flow on the way home, once I connected this hose it ran alot better. Could someone please tell me what this is I connected and to what I connected it to. Thanks