Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 111

ISC - Genera l
ISC
(IDLE
SPEED CONTROL )
GENERA L
The ISC system controls the idle speed by means
of the ISC valve to change the volume of air
flowing through the throttle valve bypass in
accordance with signals from the ECU .
There are four types of ISC valve, as follows :
• Stepper motor typ e
• Rota
ry
solenoid type
• Duty-control ACV (air control valve) type
• On-off control VSV (vacuum switching valve)
type
Air cleane r
Iri
Ignition
switc h
Battery I i
~
Engine EC U
Sensors
BASIC CONSTRUCTION OF ISC
®
The control functions in the ISC system differ
depending on the engine.
The power steering idle-up mechanism is
controlled by a separate idle-up device (see Step
2, vol . 11 ["Steering System"] for more details) .
Since the volume of air passed through the duty-
control ACV type ISC valve and the on-off
control VSV type ISC valve is small, a separate
air valve for controlling the greater amount of
air needed during cold starting is also provided .
See page 65 for details on this air valve .
OHP 69
99