Description
NCEC0279
SYSTEM DESCRIPTION
NCEC0279S01
Sensor
Input Signal to ECM
ECM func-
tion
Actuator
Camshaft position sensor
Engine speed
ECM
IACV-AAC valve
Engine coolant temperature sensor
Engine coolant temperature
Ignition switch
Start signal
Throttle position sensor
Throttle position
PNP switch
Park/Neutral position
Air conditioner switch
Air conditioner operation
Power steering oil pressure switch
Power steering load signal
Battery
Battery voltage
Vehicle speed sensor or ABS actuator and
electric unit (control unit)
Vehicle speed
Cooling fan
Cooling fan operation
Electrical load
Electrical load signal
This system automatically controls engine idle speed to a specified
level. Idle speed is controlled through fine adjustment of the
amount of air which by-passes the throttle valve via IACV-AAC
valve. The IACV-AAC valve changes the opening of the air by-pass
passage to control the amount of auxiliary air. This valve is actu-
ated by a step motor built into the valve, which moves the valve in
the axial direction in steps corresponding to the ECM output sig-
nals. One step of IACV-AAC valve movement causes the respec-
tive opening of the air by-pass passage. (i.e. when the step
advances, the opening is enlarged.) The opening of the valve is
varied to allow for optimum control of the engine idling speed. The
crankshaft position sensor (POS) detects the actual engine speed
and sends a signal to the ECM. The ECM then controls the step
position of the IACV-AAC valve so that engine speed coincides with
the target value memorized in ECM. The target engine speed is the
lowest speed at which the engine can operate steadily. The opti-
mum value stored in the ECM is determined by taking into consid-
eration various engine conditions, such as during warm up,
deceleration, and engine load (air conditioner, power steering, cool-
ing fan operation and electrical load).
COMPONENT DESCRIPTION
NCEC0279S02
The IACV-AAC valve is operated by a step motor for centralized
control of auxiliary air supply. This motor has four winding phases
and is actuated by the output signals of ECM which turns ON and
OFF two windings each in sequence. Each time the IACV-AAC
valve opens or closes to change the auxiliary air quantity, the ECM
sends a pulse signal to the step motor. When no change in the
auxiliary air quantity is needed, the ECM does not issue the pulse
signal. A certain voltage signal is issued so that the valve remains
at that particular opening.
SEF937W
DTC P0505 IDLE AIR CONTROL VALVE (IACV) —
AUXILIARY AIR CONTROL (AAC) VALVE
SR20DE
Description
EC-263