Hyundai Sonata 1991 Shop Manual page 247

MPI SYSTEM
Idle Speed Control (lSC) System
Y31DG3A
The ISC system provides the following four modes of control.
ECU
.---- +--{)
Motor
drive signal
.--------------j---oMotor
drive signal
Engine speed sensor
Coolant temperature sensor
Ignition switch-5T terminal
Air conditioner switch
Vehicle-speed sensor
Inhibitor switch
(Vehicles with an
automatic transaxle only)
.-----+--+--oldIe switch
.------------,--I-<JSensor
power supply
.------------jf-----!---oSensor
power supply
.--------!---+--oMotor
position sensor
MPS
Extension
side
L--------jf------j--I--oThrottle
position sensor
Retraction
side
L
4
-j_o--,
Sensor ground
31Y012
(a) Start Control
The throttle valve opening is controlled to optimum position for start according to the engine coolant temperature
and the altitude (atmospheric pressure).
(bl Fast Idle Control
When the idle switch is on, the engine speed is controlled to a target rpm according to the engine coolant
temperature (rpm feedback control).
When the idle switch is off, the ISC servo is actuated to move the throttle valve to a target opening position
(throttle valve opening position) according to the engine coolant temperature (target opening control).
(c) Idle Control
When the air conditioner switch is turned on or when the transmission is shifted from N to D (vehicles with
an automatic transmission), the system causes the idle speed to increase to the target rpm according to the
load (rpm feedback control).
When there is a load fluctuation (such as when the air conditioner is switched ON, etc.), there is control to
the target position (throttle valve opening) before rpm feedback control, eliminating an rpm drop due to time
lag. (target opening control)
(d) Dash Pot Control
The system provides dash pot control according to deceleration conditions to alleviate shock at deceleration.
31-22