A properly working Oxygen Sensor is essential to a proper running engine.
When your Oxygen Sensor is bad your engine may be hard to start, idle rough, increase in fuel consumption, hesitate when accelerating or climbing hills and stalling may even occur from a bad oxygen sensor.
The oxygen sensor controls the timing, fuel to air mixture and the intervals of the engines combustion.
An oxygen sensor that is bad can also cause an engine to run too rich too.