Turbo Charger Idle Down Control

On the 3S-GTE engine, the ISCV remains at a higher idle air by-pass rate for a short period of time after high speed or heavy load operation. This strategy prevents damage to the turbocharger center shaft bearings by maintaining an elevated engine oil pressure.

All other controlled parameters for the Rotary Solenoid ISC system are the same as the with the Stepper type ISCV. Idle load stabilization is maintained when input from the neutral safety switch (NSW), headlights or rear window defogger (ELS) indicate additional engine load.

As with the Stepper type ISC system, the Rotary Solenoid system utilizes a learned idle speed control strategy. The ECU memorizes the relationship between engine rpm and duty cycle ratio and periodically updates its look up tables. Both systems utilize current supplied by the BATT terminal of the ECU to retain this learned memory. If the battery is disconnected, the ECU must relearn target step positions and duty cycle ratios.

Duty Control Air Control Valve (ACV) ISC

The Duty Control ACV is typically mounted on the intake manifold. It regulates the volume of air by-passing the closed throttle valve by opening and closing an air by-pass. Valve opening time is a function of a duty cycle signal received from the ECU.

The ACV is incapable of flowing large volumes of air; therefore, a separate mechanical air valve is used for cold fast idle on engines equipped with this system.

The Duty Control ACV consists of an electrical solenoid and a normally closed (N/C) valve which blocks passage of fresh air from the air cleaner to the intake manifold. The ECU controls the valve by applying a 10 Hz variable duty ratio to the solenoid, causing the valve to pass varying amounts of air into the manifold. By increasing the duty ratio, the ECU holds the air by-pass circuit open longer, causing an increase in idle speed.

Duty Control ACV ISC Applications and Control Parameters

ISC Type/ Engine

Relevant Inputs

Controlled Parameters

Duty Control

Engine speed (Ne)

• Warm Curb Idle

VSV Type

Coolant temp. (THW)

Air conditioner clutch (A/C)

• Engine Starting

• 4A-FE

Electrical load (ELS)


• 5E-FE

Throttle signal (IDL)

Vehicle speed (SPD)

• Automatic Transmission

Neutral switch (NSW)


• Air Conditioner Idle-up

• Electrical Load Idle-up

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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