IDLE AIR CONTROL (IAC) OPERATION [LF]

B3E014018881T09

Determination of IAC valve energization time

• The PCM determines the duty signal sent to the IAC valve that corresponds to the calculated intake air amount (IAC target air amount) necessary to regulate idle speed.

• The IAC 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 valve is fixed at the minimum value and the IAC valve closes.

• When the engine is being cranked, the energization time of the IAC valve is set 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 mass).

Required volume airflow
- The required volume airflow is the calculated amount of intake airflow according to the change in intake airflow amount due to the difference in negative pressure that occurs before and after the throttle valve based on the target charging efficiency, and the change in intake air density occurring with the change in intake airflow 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 determined by the engine coolant temperature.
* :
The charging efficiency is the ratio of the actual amount of intake air to the maximum air charging amount of the cylinder mass.This value is large 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 timecorrection
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 loadlarge correction
Dashpot correction
Prevents decrease in idle speed due to insufficient intake air amount during deceleration.
Decelerated
High engine speedlarge correction
Correction at engine start
Prevents decrease in idle speed after engine start.
After cranking and engine start
Low ECTlarge 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 temperaturelarge 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 lessvolume increase correction
Target engine speed or morevolume 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.
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 speedlarge 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 idlingaverage value of feedback correction A

Target idle speed

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

Engine operation condition

Target idle speed (rpm)

No load
650
A/C operation (medium-pressure switch off)
750
A/C operation (medium-pressure switch on)
750
Electrical load operation
700*1, 750*2

*1 :
Under the condition when the electrical load is 38-48 A.
*2 :
Under the condition when the electrical load is 48 A or more.

Inhibition condition

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