Help, I'm a moron. O2 sensor...
 

So, my car (86GXL) is running a little crappy lately and after a tune up, I realize that the O2 sensor on the back of the exhaust manifold is not connected to anything. Just a little stub of a wire is hanging out.
This is wrong, right? I looked through my Haynes and found NOTHING for the O2 sensor. Is it supposed to connect to the back of my intake? There is a mysterious wire that is hanging down and I'm pretty sure that it is the one that is supposed to connect, but I wanted to get some feedback from people with RX7's.
Does the O2 sensor effect performance?

You will not notice any difference in performance with the O2 sensor reconnected, but will get a small improvement in fuel economy.