Describe the idle speed control function of an electronic control module with neat sketch.

Describe the idle speed control function of an electronic control module with neat sketch.
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Answer :

Idle Speed Control System as Output Function of ECM: While the engine is being started, or operated, the logic module of Electronic Control Module (ECM) will signal the Stepper motor of Idle Speed Control (ISC) valve to provide the easy starting without the operator having to touch the accelerator pedal. 

1. When the engine is cold, the logic module will position the AIS motor to provide the correct cold fast idle speed. The ISC valve motor allows more air to flow past the motor plunger into the intake manifold to increase the idle speed. This air flow bypasses the throttle. 2. The ISC valve motor will provide the correct idle speed when the air conditioner is on and required air: fuel mixture when the engine is decelerating. 3. The injection time is extended to provide additional fuel for cold start and during the post-start and warm up phases. The idle speed is controlled by a stepper motor, which is signalled by ECM as a function of engine speed, load and engine temperature. 4. The stepper motor controls the idle passage size to change the amount of air entering the intake manifold. Thus it controls the effective air: fuel ratio. 5. Stepper Motor: It rotates a valve shaft either in or out. This in turn increases or decreases the clearance between the ISC (Idle Speed Control) valve and its seat, thereby regulating the amount of air allowed to pass through. The Idle speed control valve stepper motor allows 125 possible valve opening positions.

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