Donna,
Yes you can unplug the O2 sensor. If you think it's running on two
cylinders, maybe it is. See if the spark plug wires are all attached.
Sounds like you know more than your mechanic.  Dump him.
He might even have two reversed. Let me know if I can send you a picture
or diagram of their proper connections.
Good Luck,
Ken Lewis
http://neksiwel.20m.com/