* Low Voltage: The alternator's primary job is to charge the battery. A failing alternator won't charge the battery properly, leading to low voltage in the system. The car's computer and other electronic components rely on a consistent voltage supply. Low voltage can cause the engine control module (ECM) to malfunction, leading to an erratic idle or a low idle.
* Insufficient Power: The idle speed is controlled by the ECM, which relies on various sensors and actuators. A weak alternator may not provide enough power for these components to function correctly, resulting in a lower than normal idle speed.
It's important to note that while a bad alternator *can* contribute to low idle, it's not the *only* possible cause. Many other problems can also lead to low idle, such as issues with the idle air control valve, throttle body, mass airflow sensor, vacuum leaks, or problems within the engine itself. A proper diagnostic test is necessary to pinpoint the actual cause.
