IDLE AIR CONTROL (IAC) OPERATION [L8, LF, L3]

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Target throttle valve opening angle determination

• The PCM calculates the intake airflow amount required to provide idling stability (IAC target airflow amount), and according to that, determines the target throttle valve opening angle.

• When the engine is cranking, the PCM sets the IAC target airflow amount according to the engine coolant temperature, and opens the throttle valve to that set value.

IAC target airflow amount

• The IAC target airflow amount is calculated by the PCM by subtracting the estimated value for the intake airflow amount which does not pass through the throttle valve from the calculated intake airflow amount required for idling stability (required volume weight).

Required volumetric airflow amount

- The required volumetric airflow amount is calculated from the target charging efficiency as corrected by the changes in intake airflow amount (due to the difference in vacuum pressure in the areas before and after the throttle valve) and in intake airflow density (which changes according to intake airflow temperature change).

Target charging efficiency

- The target charging efficiency is the charging efficiency* required to match engine operating conditions.

- The target charging efficiency is calculated by adding all necessary corrections matching engine operating conditions to the basic charging efficiency as determined according to engine coolant temperature.

* :

Charging efficiency is the ratio of the actual intake airflow amount over the maximum amount of airflow (mass) which can fill a cylinder. This figure grows larger in proportion to the increase in engine load.


Correction	Target	Conditions	Correction amount
A/C load correction	Prevents decrease in idle speed due to A/C operation.	A/C is operating.	A/C operation time→correction
Electrical load correction	Prevents decrease in idle speed due to electrical load operation.	Idle speed during electrical load operation and under any condition during driving	High electrical load→large correction
D-range correction (ATX)	Prevents decrease in idle speed due to shifting into D-range	D-range signal is input.	Low idle speed when shifted to D range→large correction
Dashpot correction	Prevents decrease in idle speed due to insufficient intake air amount during deceleration.	Decelerated	High engine speed→large correction
Correction at engine start	Prevents decrease in idle speed after engine start.	After cranking and engine start	Low ECT→large correction
Hot engine restart correction	Prevents decrease in idle speed from hot engine restart.	Just after cranking and engine start when the ECT is 60 °C {140 °F} or more the IAT is 50 °C {122 °F} or more	High intake airflow temperature→large correction
Feedback correction A	Sets idle speed to target engine speed.	Idle speed during idling (vehicle is stopped) is over or under the target engine speed (except during test mode when the engine speed is 300 rpm or less).	Actual idle speed Target engine speed or less→volume increase correction Target engine speed or more→volume decrease correction
Feedback correction B	Sets to the target engine speed when the idle speed has decreased in the range not corrected by feedback correction A, and prevents a decrease in idle speed.	During deceleration at fully closed throttle, the engine speed is the target engine speed or more and when the feedback correction A is not performed (except during test mode).	Large difference between actual idle speed and target engine speed→large correction
Engaged coasting clutch volume increase correction	Reduces shock when the transaxle coasting clutch is engaged.	When coasting clutch is engaged.	High vehicle speed→large correction
Learning correction	Stores intake air volume changes based on differences between engines and changes due to aged deterioration, and feedback.	During feedback correction A when ECT is 85 °C {185 °F} or more.	During idling→average value of feedback correction A

Target idle speed

• The target idle speed for various engine operation conditions are as follows:

Target Engine Speed


Condition	Idle speed (rpm)
Condition	L8	LF MTX	LF ATX	L3
No load	700	650	700	650
Electrical load is on.*¹	700	700	700	700
P/S is operating.	750	700	700	700
A/C is operating.*² (Middle pressure switch OFF or Not equipped)	750	750	700	750
A/C is operating.*² (Middle pressure switch ON if equipped)	750	750	750	750

*¹ :

Headlight is on, fan switch is above 1st, cooling fan is operating, and rear window defroster is on.

*² :

A/C switch and fan switch are on.