2003 mitsubishi lancer evolution. Does this black/yellow hose line go somewhere? i found it it the back of the intake manifold unplugged.

 

it might have been used for a boost gauge by the previous owner, does it have suction when the car is on?

 

It goes to an emissions related solenoid under the intake manifold on the passenger side. There is a diagram affixed under the hood for reference. Zip tie or mini clamp it to prevent it from blowing off in the future.

 

+1