IDLE AIR CONTROL (IAC) OPERATION [L3 R.H.D.]

BUE014000000N09

IAC Solenoid Valve Operation Principle

1
Single cycle
2
Energization time

• The PCM operates the IAC solenoid valve with a duty signal. The duty signal uses a given frequency to vary the energization period of the IAC solenoid valve during a single cycle and the length of this period determines the IAC solenoid valve opening angle.

Determination of IAC Solenoid Valve Energization Time

• The PCM determines the duty signal sent to the IAC solenoid valve that corresponds to the calculated intake airflow amount (IAC target airflow amount) necessary to regulate idle speed.
• The IAC solenoid valve receives the duty signal from the PCM which moves the plunger, and by adjusting the surface area of the opening, the idle speed is controlled to the target speed.
• When the ignition switch is turned to the ON position, the energization time of the IAC solenoid valve is fixed at the minimum value and the IAC solenoid valve closes.
• When cranking the engine, the energization time of the IAC valve is set according to the engine coolant temperature and the valve opens as much as the set value.
IAC target airflow amount
• The target IAC airflow amount is the estimated value of intake air amount that does not pass through the IAC valve (airflow amount flowing from the gap in the throttle valve) subtracted from the intake airflow amount required to regulate idling as calculated by the PCM (required volume airflow).
Required volume airflow
- The required volume airflow is the intake airflow amount which is calculated from the target charging efficiency based on the variation in intake air amount due to the difference in negative pressure that occurs before and after the throttle valve, and the variation in intake air density occurring with changes in intake air temperature.
Target charging efficiency
- The target charging efficiency is the charging efficiency* required for the engine operation conditions.
- The target charging efficiency is calculated by adding the corrections according to engine operation conditions to the basic charging efficiency, which is determined according to the engine coolant temperature.
* :
Charging efficiency is the ratio of the actual amount of intake air to the maximum air charging amount (mass volume) of the cylinder. This value increases proportionately to the increase in engine load.

Correction

Target

Condition

Correction amount

A/C load correction
Prevents drop in idle speed due to A/C operation.
A/C on
During A/C operation→correction
P/S load correction
Prevents drop in idle speed due to P/S operation
P/S operation
During P/S operation→correction
Electrical load correction
Prevents drop 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
Prevents drop in idle speed due to shifting into D-range
D range signal (TR switch) input
If difference between idle speed and turbine speed during D-range signal input is large →large correction
Dashpot correction
Prevents drop in idle speed due to insufficient intake air amount during deceleration.
Decelerated
High engine speed→large correction
Correction at engine start
Prevents drop in idle speed after engine start.
Immediately after cranking and engine start
Low engine coolant temperature→large correction
Hot engine restart correction
Prevents drop in idle speed due to hot engine start.
Just after cranking and engine start when the engine coolant temperature is 60°C {140°F} or more
High intake airflow temperature→large correction
Feedback correction A
Sets idle speed to target engine speed.
Idle speed while idling (vehicle stopped) is over or under the target engine speed (except during test mode when 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 to 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.
Coasting clutch engaged
High vehicle speed→large correction
Fuel cut recovery reduction correction
Lessens shock at fuel cut recovery
Fuel cut recovery
Large difference between actual idle speed and target engine speed→large correction
Learning correction
Stores intake air amount changes based on differences between engines and deterioration over time, and feedback.
During feedback correction A when engine coolant temperature is 85°C {185°F} or more and intake air temperature is 85°C {185°F} or less.
While idling→average value of feedback correction A

Target Idle Speed

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

Engine operation conditions

Target idle speed (rpm)

P or N position

Not P or N position

A/C on
700
700
Electrical load operation (Low)
700
650
Electrical load operation *(High)
700
700
P/S operation
700
700
No load
650
600

* :
The headlights, rear window defroster, blower fan (level 2 or more), main fan and additional fan are operating

Inhibition condition

• If the IAC solenoid valve is damaged (when DTC P0511 is detected), power to the IAC solenoid valve is cut (IAC solenoid valve closes) preventing a sudden increase in engine speed.