EgonzEk

hey looking for some help. my 2000 ek is throwing my check engine light when i'm in either third or fourth gear cruising. I only does it once in a while and gives me codes for my O2 sensor. i had been running my car for about two years without the second O2 sensor connected to the cat, and then out of nowhere i started having the problem. do you guys think i should just hook it back up or replace it. im just running basic bolt ons..