Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 119

ISC - Functions of Engine EC U
FEEDBACK CONTRO L
Feedback control is carried out when the idle
contact is on, the vehicle speed is below a
predetermined speed, and the coolant
temperature is about 80°C (176°F) .
If the difference between the actual engine
speed and the target speed stored in the
memory of the ECU is more than 20 rpm, the
ECU sends a signal to the ISC valve, telling it to
increase or decrease the volume of air passing
through the bypass passage so that the actual
engine speed will match the target speed .
125
A-B : After-sta
rt
control
B-C : Warm-up control
C-D : Feedback control
1 1 k
ENGINE
SPEED CHANGE ESTIMATE CONTRO L
Immediately after the neutral start switch or air
conditioner switch is operated, the engine load
also changes . To prevent the engine speed from
changing because of this, the ECU sends signals
to the ISC valve to open or close it by a fixed
amount before changes in the engine speed can
occur .
- RELEVANT SIGNALS
• Engine speed (NE )
• Neutral sta
rt
switch (NSW)
• Thro
tt
le position (IDL)
• Vehicle speed (SPD)
• Air conditioner (A/C )
ELECTRICAL LOAD IDLE-UP CONTRO L
20 80
(68)
(176 )
A
------------------ ----------------
Coolant temperature °C (°F)
OHP 7 5
Target speeds also differ depending on engine
conditions, such as whether the neutral start
switch is on or off, and whether the air
conditioner switch is on or off.
NOTE
Stepper motor type ISC valves also control idle
up of the air conditioner .
RELEVANT
SIGNALS
• Engine speed (NE )
• Throttle position (IDL)
• Vehicle speed (SPD )
• Coolant temperature (THW)
• Air conditioner (A/C )
• Neutral sta
rt
switch (NSW)
Since the generating capacity of the alternator in-
creases when an electrical load is applied, the
Engine ECU opens the step position by a certain
number of steps in order to increase the idle speed
when there has been a voltage drop at the + B ter-
minal or IGSW terminal or when a signal has been
applied to the LP terminal, DFG terminal or ELS ter-
minal .
RELEVANT SIGNAL S
• Electrical load (LP, DFG, or ELS)
• Engine speed (NE )
• Throttle position (IDL)
• Vehicle speed (SPD )
OTHER CONTROL S
In addition to the above controls, some engines
are also provided with a control in which the ISC
valve operates like a dashpot during
deceleration, and a control in which the ISC
valve opens slightly when the oil pressure
switch goes on .
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