Idle Speed/Throttle Actuator - Electronic: Description and Operation

IDLE AIR CONTROL SYSTEM [FS]
^ The PCM carries out idle air control through the following modes.
i. Deceleration mode
ii. Closed loop control mode

Deceleration mode (i.e. closed or partially closed throttle)
^ During deceleration the PCM enables the IAC to adjust air flow to the throttle body to prevent engine stalling.

Closed loop control mode
^ The following conditions must be met for idle air control in closed loop control mode.
i. The vehicle speed is below 4 km/h 12.5 mph.
ii. The PCM determines the neutral condition based on the input by the neutral/clutch switch. (MTX only)
^ The purpose of closed loop control mode is to maintain engine stability when idle through feedback control.

Adoptive air compensation
^ The PCM memorizes the idle air trim level required to maintain the target engine speed. When the following conditions exist, the PCM prohibits adaptive air compensation.
i. During closed loop control mode.
ii. During no load condition (Neutral [MTX], N position [ATX]) instead of the closed loop control.(When changes of engine speed are above specification)
iii. When it does not meet condition (1) or (2) above, and the charging efficiency is below the specified value.
^ When the idle air trim correction is above the specified value, the PCM judges the malfunction in the idle air control system, and stores a DTC.
^ If the Keep Alive RAM has been reset, the idle air trim learning correction is also cleared, the engine must idle for 15 minutes at each of the following four separated modes to learn the new idle air trim.





Target engine speed





^ The optimum engine speed at idle as shown in the table.





Block Diagram

Idle Air Control (IAC) Valve Description
Function
^ The IAC valve controls the amount of the bypass air that passes through the throttle valve IAC controlled by a PCM signal.
^ The air, which bypasses the throttle valve, flows through the IAC valve from inlet port (air hose side) to outlet port (intake manifold side).

Structure
^ IAC valve is composed of a housing, plunger, coil and spring.

Operation








^ When the IAC valve receives a signal from the PCM, the electric current is applied to the coil circuit. The plunger is then pulled back to allow bypass air into the outlet port.
^ The bypass air flow is controlled by the period of time that current is applied to the coil circuit. This current opens the plunger, allowing bypass air into the outlet port.