That's either the VFAD connector or the vac line for the intake manifold solenoids. If it's the first you want the loose end to connect to a tube on / near the air filter box, which then continues to the front of the car under the bumper cover. If it's the second, that loose end needs to go to what looks like a black tank between the firewall and the intake manifold, with 3 electrical connections on it. It's a bit harder to get to for sure. The check valve (green/white thing) has an arrow on it. That arrow needs to be in the direction of the intake manifold (which is where the connected end of that line should be connected, and looks already is)

 

The orange line is the VFAD vacuum line if your car is a series 1 (04-08). Someone may have installed an aftermarket intake and cut this line or unplugged it, For now make sure the vacuum line inlet on the intake manifold is capped off where the diagram says "cap VFAD here" or it will suck debri into the intake manifold.