Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 122

ISC - Functions of Engine EC U
3 . DUTY-CONTROL ACV TYPE ISC VALV E
The duty-control ACV controls the volume of air
passing through the throttle valve by means of
signals (duty signals) from the Engine ECU, and
is mounted on the intake manifold . The air flow
volume is determined by the ratio of the length
of time that the air flow volume signal from the
ECU is on to the length of time that it is off .
If the idle speed has dropped due to changes in
engine running conditions or changes in the
electrical load (as when the air conditioner
switch or neutral start switch is operated, etc .),
the ACV controls the volume of air bypassing
the throttle valve according to signals from th e
Battery
ECU, thus helping to stabilize the idle speed .
(During warm-up, the fast-idle speed is
controlled by the air valve .) Control is as
explained below .
NOT E
Connecting the T (or TE1) terminal to the El
terminal of the check connector or TDCL
causes the ECU to fix the ACV opening angle
to a certain value, regardless of engine
operating conditions .
OHP 7 7
STARTING CONTRO L
To improve startability during cranking, STA
goes on, causing the ACV to open fully .
RELEVANT SIGNA L
• Ignition starter switch (STA )
FEEDBACK CONTRO L
The ECU changes the duty ratio of the V-ISC
signal to maintain the idle speed under
conditions other than starting control, engine
speed change estimate control, and constant
duty control .
-RELEVANT SIGNAL
• Engine speed (NE )
• Coolant temperature (THW)
ENGINE SPEED CHANGE ESTIMATE CONTROL
The duty ratio changes when the air conditioner
switch or neutral start switch is operated . This
helps to limit changes in the idle speed .
- RELEVANT SIGNAL S
• Neutral sta rt switch (NSW)
• Air conditioner (A/C )
CONSTANT DUTY CONTRO L
The ECU maintains the ACV at a fixed opening
angle when the idle contact is off or the air
conditioner switch is on .
RELEVANT SIGNALS
• Throttle position (IDL)
• Air conditioner (A/C )
110