Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 118

ISC - Functions of Engine EC U
AFTER-START CONTRO L
Due to the previous set-up of the ISC valve, the
amount of air passing through the ISC valve
during starting is the maximum amount possible .
This allows the engine to start easily .
However, after the engine has started, its speed
would rise too high if the ISC valve were kept
fully open, so when the engine reaches a certain
speed (this speed being determined by the
temperature of the coolant) during or after
starting, the ECU begins sending signals to the
ISC valve, causing it to close from step 125 (fully
open) to a point determined by the coolant
temperature .
For example, if the coolant temperature is 20°C
(68°F) during starting, the ISC valve will
gradually close from the fully-open position
(step 125, or point A) to point B when engine
speed reaches the predetermined level .
125
A
A-B : After-sta
rt
contro l
20
(68 )
Coolant temperature °C (°F )
RELEVANT
SIGNALS
• Engine speed (NE )
• Coolant temperature (THW)
• Throttle position (IDL )
• Vehicle speed (SPD)
OHP 75
WARM-UP (FAST-IDLE) CONTRO L
As the coolant warms up, the ISC valve
continues to gradually close from the point to
which it closed during starting . When the coolant
temperature reaches about 80°C (176°F), fast-
idle control by the ISC valve ends .
125
A
---------- -------------
\ A-B : A
ft
er-sta
rt
contro l
B-C : Warm-up contro l
20 80
(68) (176 )
Coolant temperature °C (°F)
OHP 7 5
r--
RELEVANT SIGNAL S
Engine speed
(NE )
Coolant temperature (THW)
Throttle position (IDL)
Vehicle speed (SPD )
106