Disconnect O2 Sensor?
 

I read so much about disconnecting the O2 Sensor. I guess my head still keeps asking why does it exist and what are the pros/cons of disconnecting it (other than not being able to pass emmissions tests)?

If the O2 sensor is disconnected, the DME computer operates in Open Loop mode. In this case, the DME simply proves the fuel by determining the amount of air flow into the engine and selecting the appropriate amount of fuel from a set of preset fuel maps.
You'll get these...
Engine surges or hesitates
Strong smell of gas from the exhaust
Poor fuel economy
Failed emissions due to high CO or high HC levels
Catalytic converter (if equipped) becomes prematurely clogged

And you may get a check engine light. It's a necessary part of the emissions control system and Zef covered it thoroughly. You need it for optimal engine efficiency.

As noted, the O2 circuit basically corrects the amount of fuel that the basic fuel map is delivering to a level best for emissions and basic fuel economy. It also compensates for difference between motors, maintenance, and environment that the basic map or system can not account for.

Unplugging it takes this correction out of the equation. In some cases running on the basic map without the correction will improve performance.

I believe the Controller also looks at the rate of change in air flow. When it senses moderate acceleration it may postpone the O2 correction.

When the throttle is floored and the Wide Open Throttle switch is engaged, the O2 correction is taken out of the equation and the WOT map determines fuel at a level about 10% richer to achive max torque instead of efficient combustion.

Basically, by unplugging the O2 you are making the car operate like most of the Euro cars.

I think a better approach to unpluging is make sure you car is in good tune and spec. Then add a 911Chips.com chip.

Might help if you let us know if your car is an SC or a later Carrera.