3-22 ENGINE CONTROL SYSTEM
Duty cycle signal for IAC valve
(example: 25% duty)
“ON” time
1 cycle time
× 100 = duty (%)
OFF
ON
25 ms
100 ms (1 cycle)
Time
CONTROL MODE
BEFORE START:
The IAC valve is closed (0% duty) when engine is not running.
WHEN CRANKING:
The IAC valve is controlled to operate at 100% duty.
AFTER START (FAST-IDLE FUNCTION):
The IAC valve is controlled to operate at approx. 25 – 100% duty until the timer, which was set according to
cylinder temperature at cranking, expires.
WHEN IDLING / TROLLING:
The IAC valve is controlled so that the engine speed is stable at the idling / trolling speed specified.
During this period, the IAC valve has a duty cycle of approx. 22.5% but will vary slightly as idling / trolling
conditions change.
WHEN RUNNING (NORMAL OPERATION):
The IAC valve is controlled to operate at 20 – 100% duty, which depends on the current engine conditions.
WHEN DECELERATING (DASH-POT EFFECT):
When the throttle valve is suddenly returned to full close and the CTP switch signal changes to “ON”, the IAC
valve operates at a controlled gradual return to idle / troll operating duty to prevent engine stalling or unstable
running.
NOTE:
Due to the limited intake air flow from the IAC passage and in order to effectively use both the “Dash-pot
effect” and “Fast-idle function”, the by-pass air screw must be adjusted to provide IAC valve operation at
approx. 22.5% duty at the engine idling / trolling specification.
See the page 2-14 for the by-pass air screw adjustment procedure.
Battery
charge
coil
Rectifier &
regulator
30A fuse
Battery
ECM
CPU
Sensor/switch
signal input
ECM
main
relay
Ignition
switch
15A
fuse
IAC valve
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