Learned Idle Speed Control

The idle speed control program is based on an ECU stored look up table which lists pintle step positions in relation to specific engine rpm values. Over time, engine wear and other variations tend to change these relationships. Because this system is capable of feedback control, it is also capable of memorizing changes in the relationship of step position and engine rpm. The ECU periodically rewrites the look up table to provide more rapid and accurate response to changes in engine rpm.

Idle Control Valve Toyota Yaris

The Rotary Solenoid ISCV is mounted to the throttle body. This small, lightweight and highly reliable valve controls the volume of intake air which is allowed to by-pass the closed throttle valve. Air volume control is accomplished by means of a movable rotary valve which blocks or exposes the air bypass port based on signals received from the ECU.

The valve assembly consists of two electrical coils, a permanent magnet, a valve and valve shaft. A fail-safe bi-metallic coil is fitted to the end of the shaft to operate the valve in the event of electrical failure in the ISCV system.

Morris Minor Alternator Wiring

Because the Rotary Solenoid ISCV has large air volume capability, it is used to control cold fast idle as well as other idle speed parameters. Although this ISCV is not used in combination with a mechanical air valve, models equipped with air conditioning do require the use of a separate A/C idle-up device.

The ECU controls movement of the valve by applying a 250 Hz duty cycle to coils T1 and T2. The electronic circuitry in the ECU is designed to cause current to flow alternately in coil T1 when the duty cycle signal is low and in coil T2 when the signal is high. By varying the the duty ratio (on time compared to off time), the change in magnetic field causes the valve shaft to rotate.



As duty ratio exceeds 50%, the valve shaft moves in a direction that opens the air bypass passage. At a duty ratio less than 50%, the shaft moves in a direction which closes the passage. If the electrical connector is disconnected or the valve fails electrically, the shaft will rotate to a position which balances the magnetic force of the permanent magnet with the iron core of the coils. This default rpm will be around 1000 to 1200 rpm once the engine has reached normal operating temperature.

Rotary Solenoid ISC System Applications and Control Parameters

ISC Type/ Engine

Relevant Inputs

Controlled Parameters

Rotary Solenoid

Engine speed (Ne)

• Warm Curb Idle


Throttle angle (IDL)

• 4A-GZE

Vehicle speed (SPD)

• Cold Fast Idle

Coolant temp. (THW)

• 2TZ-FE

Neutral/Start switch (NSW)

• Electrical Load Idle-up

• 3S-GTE

Ignition switch (STA)

• Automatic Trans

• 3S-FE

Electrical Load (ELS)

mission Idle-up

• 5S-FE

Battery voltage (+B)

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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  • Katri Kiri
    What can be the main reason for failed idle speed on a 5s engine?
    12 months ago
  • berilac
    Why high and low idle relay is important in idl?
    10 months ago

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