A bad oxygen sensor can negatively impact an engine's performance in a variety of ways. Because of the important role an oxygen sensor plays in the maintenance of proper air and fuel levels in a running engine, any abnormal or faulty oxygen sensor function can create several abnormal engine symptoms.
Poor Gas Mileage
Oxygen sensors play a huge role in adjusting a vehicle engine's air/fuel ratio, the combination of gas and air an engine burns to produce power. A faulty oxygen sensor may allow too much fuel to be added to the air/fuel ratio, resulting in poor gas mileage.
Increased Vehicle Emissions
Oxygen sensors monitor and adjust an engine's air/fuel mixture to ensure proper engine combustion, vehicle emissions and performance. A bad oxygen sensor can result in poor air/fuel mixtures or lean or rich fuel-injection delivery, all of which can cause improper or inefficient engine combustion and increased vehicle emissions.
Rough Engine Idle
Proper engine combustion is crucial for maximising engine performance. A bad oxygen sensor can cause a car's engine to idle in a choppy, rough manner. This is caused by the less-than-optimum engine combustion firings that result in poor engine performance.
If a bad oxygen sensor causes an engine's air/fuel mixture to become too lean or restricted, the explosions within an engine's cylinders (engine combustion) will be altered. Normally, an air/fuel mixture that is too lean (too much air, not enough fuel) will cause an engine to miss, or misfire, especially when an engine is idling.
Engine hesitation is similar to engine missing. However, engine hesitation is experienced only during acceleration, while an engine miss can be experienced both during engine acceleration and idle. A bad oxygen sensor may misread or misinterpret an engine's air/fuel mixture or air/fuel requirements and cause too little or too much air and/or fuel to enter an engine's cylinders, especially during acceleration. This can cause an engine to hesitate, or stumble.