Did some looking at the line, and I see the soft EVAP hose goes from the brake booster to the big wire loom, where there is a hard EVAP line connector, the line comes out of the big loom above the heater hoses area, you have to remove that cover to see it, the soft EVAP line connected to that goes to some sort of diaphragm, then another piece of soft hose runs from the other end of that diaphragm, that soft hose connects to another hard EVAP T connector that is in the smaller wire loom in that area, where one part of it appears to go in right where the heater area is, by the hoses.
The other part of that line runs through that smaller loom, it goes by/around the coolant recovery tank area, than up under the headlights area, where it runs under the front of the car till it gets up under the air filter/PCM tray.
I'll have to remove my air filter cover later, that way I can see just where the line connects, I have an idea, but want to be sure..
Hopefully that helps a little, I'll attach the pics of the line where it is near the heater hoses area.
So it sounds like Mike was right about it being the EVAP for the HVAC controls.