An idle air control motor (IAC) is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or PCM (powertrain control module) receives information from various sensors and will output signals to adjust the idle air control motor in or out to adjust engine idle speed by controlling engine idle air. In order to adjust the idle RPM of an engine, the cars need an IAC to control the speed of the electrically-operated valve, which is functioned as the manager of throttle body. In other words, IAC regulates the idle speed of engines.
The common problems of the idle air control motor (IAC) is that it is highly susceptible to carbon and coking build up. In other words, if an idle air control goes too long without cleaning, it can cause stalling and poor idle quality. Some cars are designed with a large vacuum transfer hose that connects the intake manifold to the idle air control motor. Inspect all engine and accessory vacuum lines to look for missing, torn or dilapidated lines and replace as needed. Any car that is designed with a magnetic non-motor operated idle air control like Toyota and Lexus is subject to carbon and should be cleaned about every 40,000 miles to avoid stalling.