IDLE AIR CONTROL (IAC) OPERATION [F2]

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Duty Control

Operation outline

• For optimum idle air control, the PCM selects one of the target airflows preset in the PCM according to the engine conditions, and converts the target airflow into the IAC valve actuation time to controls the vale operation.

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IAC valve actuation time

• IAC valve actuation time is determined by the target airflow.

Target airflow

• The target airflow is calculated using the following formula:

Target airflow = Mass intake airflow × ECT correction coefficient × B+ correction coefficient

• As the mass intake airflow varies with the engine conditions, correction is made by applying various correction coefficients.

• The ECT correction coefficient and the B+ correction coefficient are used for density correction when converting the mass intake airflow amount. The ECT correction coefficient is determined by the engine coolant temperature, and the B+ correction coefficient is determined by the battery positive voltage.

Control Zone

Control outline

• For optimum idle air control the PCM divides the control into four zones according to the engine speed and conditions of the CTP switch and terminal TEN. The duty value is decided on the target airflow that is preset in the PCM according to the engine conditions.

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Start zone

• The control is in start zone when the engine is cranking and the engine speed is below 500 rpm.

• Target airflow in the start zone is calculated by replacing the mass intake airflow with the mass intake airflow at start.

• The mass intake airflow at start determined according to the engine coolant temperature and barometric pressure.

Initial setting zone

• The control is in the initial setting zone when terminal TEN grounded.

• Target airflow in the initial setting is calculated by replacing the mass intake airflow with the mass intake airflow at initial setting.

• The mass intake airflow at initial setting determined according to the engine coolant temperature and barometric pressure.

Closed loop zone

• Closed loop correction adjusts the idle speed to the target according to the ECT and engine load conditions. This correction is carried out when the CTP switch is on and the gear is not engaged.

• The mass intake airflow for the closed loop zone is calculated using the following formula:

Mass intake airflow = BARO correction × Basic mass airflow + After-start correction +

Load correction + Dashpot correction + Deceleration volume increase correction ±

Closed loop correction ± Learning correction

• The basic mass airflow is determined by the engine coolant temperature.

Open loop zone

• The control is in the open loop zone when it is in other than the above zones.

• The mass intake airflow for the open loop zone is calculated using the following formula:

Mass intake airflow = BARO correction × Basic mass airflow + After-start correction + Load Correction +

Dashpot correction + Deceleration volume increase correction -

Acceleration volume decrease correction ± Closed loop correction ± Leading correction

Corrections

Item

Purpose

Conditions

Action

BARO correction

To adjust intake air amount according to BARO change

According to BARO

Lower BARO → Larger correction

After-start correction

To stabilize engine speed just after engine start

Just after engine start

Lower ECT → Larger correction

Lower IAT → Larger correction

Load correction

To stabilize engine speed when A/C or P/S operating

A/C or P/S turned on

Heavier load → Larger correction

Dashpot correction

To reduce deceleration shack and CO and HC emission Leaves during deceleration

Just after deceleration at CTP

High engine speed → Larger correction

Deceleration volume increase correction

To reduce engine speed drop when decelerating

When deceleration (Throttle opening angle variation large)

Deceleration → Set amount of correction

Acceleration volume decrease correction

To reduce sudden engine speed increase when accelerating

When accelerating (Throttle opening angle variation large))

Acceleration → Set amount of correction

Closed loop correction

To bring engine speed to target speed

When in closed loop zone and open loop zone

Larger difference → Larger correction

Learning correction

To correct target speed

When in closed loop zone and open loop zone

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Item	Purpose	Conditions	Action
BARO correction	To adjust intake air amount according to BARO change	According to BARO	Lower BARO → Larger correction
After-start correction	To stabilize engine speed just after engine start	Just after engine start	Lower ECT → Larger correction Lower IAT → Larger correction
Load correction	To stabilize engine speed when A/C or P/S operating	A/C or P/S turned on	Heavier load → Larger correction
Dashpot correction	To reduce deceleration shack and CO and HC emission Leaves during deceleration	Just after deceleration at CTP	High engine speed → Larger correction
Deceleration volume increase correction	To reduce engine speed drop when decelerating	When deceleration (Throttle opening angle variation large)	Deceleration → Set amount of correction
Acceleration volume decrease correction	To reduce sudden engine speed increase when accelerating	When accelerating (Throttle opening angle variation large))	Acceleration → Set amount of correction
Closed loop correction	To bring engine speed to target speed	When in closed loop zone and open loop zone	Larger difference → Larger correction
Learning correction	To correct target speed	When in closed loop zone and open loop zone	—