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Deceleration device

Deceleration device


The task of the deceleration device is to prevent emission of unburnt hydrocarbons during engine braking. It is built into the IAC valve.

The IAC valve

The IAC valve was introduced to give:


• a more even engine speed

• better cold starting and warm running characteristics,

• increased engine speed when the air-conditioning unit is switched on,

• compensation for the lowering of the engine speed due to increased load from steering servo-pump, generator charging and when driving at high altitudes,

• deceleration function.

The IAC valve regulates the air-flow which passes the butterfly. The volume of the air-flow is determined by the degree of opening of the valve, which is controlled by signals from the engine control module. In this way the amount of air required on each occasion is allowed to pass in order to maintain a constant idling speed.

The IAC valve is a motor-driven sliding valve which is powered from a PWM outlet on the engine control module. The valve can go from closed to fully open in 0.2 seconds. The reciprocating movements are hardly visible.