This one stubborn hose refuses to go into the main air intake tube that goes into the airbox for my 2005 R53 automatic.
I don't know what it leads to or what it's for, if it's critical to engine operation. Right now its sort of half in the intake tube, it's so difficult to get it into where it's supposed to go.

It was popped out this morning when I went to add some more oil. :/


Hose marked with red line

 

That looks heater hose size to me. The air box has two larger air hoses. If you get it off have a drain pan on hand.

 

It's more that I want to get it back on, I never meant to take it off in the first place. I think it slipped out while changing the air filter.

 

Believe its the PCV valve hose (goes into valve cover). You need to clamp it and close to the end since not much of the hose is on the nipple coming out of the intake tube.
Easy to knock off when you are twisting on the tube getting the top of the airbox off