If an engine has a rough idle and the A/F ratio is fluctuating excessively, what component might be failing?

When an engine experiences a rough idle accompanied by an excessively fluctuating air-fuel (A/F) ratio, it indicates that there may be issues with how the engine is managing the air entering the combustion chamber. The Mass Air Flow (MAF) Sensor is crucial in determining the exact amount of air entering the engine, allowing the engine control unit (ECU) to adjust fuel delivery appropriately. If the MAF sensor is failing or providing inaccurate readings, it can lead to poor engine performance, reflected by an unstable idle and fluctuating A/F ratios.

A faulty MAF sensor can miscalculate the amount of air entering the engine, resulting in either too much or too little fuel being injected. This imbalance directly contributes to the rough idle condition and the noticeable fluctuations in the A/F ratio.

While other components, such as the throttle position sensor, intake air control valve, and fuel injectors, can also impact idle quality and A/F ratios, they typically manifest in different ways or lead to specific engine performance issues that differ from those caused by MAF sensor failure. Thus, when faced with the symptoms of a rough idle and fluctuating A/F ratio, the most likely culprit to investigate first is the MAF sensor.