Idle Speed/Throttle Actuator - Electronic: Description and Operation

This system controls the bypass air flow by means of ECM and idle air control valve (IAC valve) for the following four purposes.
- To keep the engine idle speed as specified at all times. The engine idle speed can vary due to following reasons.
- Load applied to engine (when electric load is applied, automatic transmission is shifted to "R", "D", "2" or "L" range, A/C is turned ON, etc.)
- Variation in atmospheric pressure
- Change in engine itself with passage of time
- Other factors causing idle speed to change
- To improve starting performance of engine
- To compensate air/fuel mixture ratio when decelerating (Dash-pot effect)
- To improve driveability while engine is warmed up.











Operation
Opening of IAC valve is controlled according to IAC valve opening signal and closing signal sent from ECM. ECM detects the engine condition by using the signals from various sensors and switches and controls the bypass air flow by changing the current flow time ratio between the time (To) within a cycle during which electricity flows through the IAC valve opening coil (i.e., IAC valve moves in its opening direction) and the time (Tc) during which electricity flows through the IAC valve closing coil (i.e., IAC valve moves in its closing direction). When the vehicle is at a stop, the throttle valve is at the idle position and the engine is running, the engine speed is kept at a specified idle speed.