I bought a 1990 RX-7 NA and I've come across a random hose on the back of the motor that I don't know where it goes. The car runs with it not connected to anything, nothing comes out of the hose, and the hose looks dry. I have no clue what this could be. The FSM doesn't seem to give a good illustration of it, either.

This photo was taken from underneath the car on the passenger side. (The trans is on the left of the pic. The holes at the bottom are the exhaust ports with the exhaust manifold removed. My finger points to the base of the mystery hose.)

The hose even has a hose clamp on the end, but there are no tubes or hoses near it that don't have something plugged into them. Help!

 

Split air pipe is my best guess. It goes to the little port on the side of the cat.

 

Thanks for the info. So if I correctly understand what the split air pipe does, since this is a S5 RX7 N/A with no cat and the air pump removed, it sounds like I can just cap this off at the base and call it a day.

 

Yes or block it off and remove it completely if it hasn't been blocked already