That line probably goes to your throttle body.

I HOPE you have a service manual for the car this engine came out of. All of your answers are in there. There will be vacuum diagrams, and coolant diagrams that will sort out all your hose problems. You don't want coolant going into ANY vacuum line, and there are both coolant and vacuum lines connected all around the intake manifold.

You'll find coolant lines on teh throttle body, AICV, oil cooler (if equipped), heater core, and overflow bottle. Vacuum lines on the throttle body, intake manifold, emissions equipment, valve cover, brake booster, and sensors. Water entering any of those parts would be horrible. Whether it's a water or vac line, it's imperative for it all to flow right in order for the systems plugged into them to work properly.