Idle Speed Control

Idle Speed Control

Once the engine has reached normal operating temperature, the idle speed is controlled by the ECM. When the idle drops below the specified idle speed (due to increased mechanical or electrical loads), the ECM indexes the IACV to restore the correct idle speed.

On return to idle, the ECM initially implements a slightly higher idle speed. This prevents the engine stalling when the throttle is closed.

NOTE: Idle speed control will only occur when the engine speed is below a predetermined set point.

Cranking Position

During cranking, the ECM indexes the IACV to a position for a ’throttle off’ start. This position is dependent upon coolant temperature and on ’T’ series only, fuel temperature.

Over-run Control

During over-run conditions, the ECM indexes the IACV, opening the throttle disc. This increases the air flow into the engine reducing hydrocarbon emissions.

Low Battery Voltage Compensation

When the battery voltage drops below a preset value, the ECM indexes the IACV increasing the idle speed, consequently increasing alternator output.