Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve (IAC valve)





Description

This idle air control valve differs from the LH 2.2 valve in that the reversible motor is replaced by a solenoid. The coil (2) receives pulse signals from the control module. When activated, the coil overcomes a mechanical spring (5) that keeps the valve closed. This allows a specific volume of air to flow past the throttle butterfly in the intake manifold.

In the event of a fault, the opening pulses terminate and the spring (5) pulls the valve to the end position. The air flow through the valve in this position (Limp Home) is greater than during normal operating conditions. This gives an idle speed of 1,200 - 1,500 rpm.

The Limp Home function is activated when a fault arises in the IAC system, such as might be caused by a loose cable.

During deceleration when the throttle butterfly is fully closed (braking), the valve is controlled by the control module so that extra air can flow past the throttle butterfly. This is to ensure complete combustion of any injected fuel. This function replaces the dashpot function in the LH 2.2 system.

Idle speed control in the LH 2.4.1 system has been further improved. This has been achieved by the addition of vehicle speed information to the control module's calculations. The signal is obtained from the speedometer.

As long as the speed of the car exceeds about 6-8 km(h, engine speed will be higher than idle speed but will drop to idle speed when this speed limit is no longer reached.

As a result, braking to a standstill is extremely smooth.





In the LH 2. .4.2 system the idle air control valve has two windings and a reversible motor. The windings partially counteract each other so that a voltage drop, such as caused by engagement of AC, does not affect control. The two windings also make for faster control.

In the event of a fault, a spring sets the valve in the Limp Home position. This position results in an engine speed of about 550 rpm when the valve is not under load.

Adaptive idle air control system, LH 2.4, 2.4.1 and 2.4.2

In the adaptive (smart) idle air control system, adjustment / setting of idle speed takes place continuously and automatically compensates for all normal changes.

The microprocessor in the control module "remembers" the opening the IAC valve had the last time the engine was running at idle speed. This system reduces the need for service and the setting is maintained unchanged at a high level.