Lexus SC300 / Lexus SC400. Manual - part 483

Idle Speed Control (ISC) Valve

ON–VEHICLE INSPECTION

INSPECT ISC VALVE FOR OPERATING SOUND

Check that there is a clicking sound immediately after stop-
ping the engine.
If the rpm operation is not as specified, check the ISC valve,
wiring and ECU.

FI–80

                  –   Air Induction System (Idle Speed Control (ISC) Valve)

EFI SYSTEM

COMPONENTS

REMOVAL OF ISC VALVE

1. 

REMOVE LOWER HIGH–TENSION CORD COVER
(See steps 1, 2 and 5 to 12 on pages 

FI–27

 to 29)

2. 

REMOVE ISC VALVE
(a)  Disconnect the ISC valve connector.
(b) (USA 

Spec.)

Remove the bolt holding the water by–pass pipe (be-
tween ISC valve and EGR valve) to the air intake cham-
ber.

(c)  (Exc. USA Spec.)

Remove the bolt holding the water by–pass pipe (be-
tween ISC valve and EGR valve) to the VSV (for fuel
pressure control).

FI–81

EFI SYSTEM   –   Air Induction System (Idle Speed Control (ISC) Valve)

(d)  Disconnect the following hoses from the ISC valve:

(1)  Water by–pass hose (from throttle valve)
(2)  Water by–pass hose (from water inlet housing)
(3)  Water by–pass hose (from EGR valve)

(e)  Remove the two nuts, ISC valve and gasket.

INSPECTION OF ISC VALVE

1. 

INSPECT ISC VALVE RESISTANCE
Using an ohmmeter, measure the resistance between the ter-
minals (B1–S1 and S3, B2–S2 and S4).

Resistance: 10–30 

If resistance is not as specified, replace the ISC valve.

2. 

INSPECT ISC VALVE OPERATION
(a)  Apply battery voltage to terminals B1 and B2, and while

repeatedly grounding S1–S2–S3–S4–S1 in sequence,
and check that the valve moves toward the closed
position.

(b)  Apply battery voltage to terminals B1 and B2, and while

repeatedly grounding S4–S3–S2–S1–S4 in sequence,
and check that the valve moves toward the open
position.

If operation is not as specified, replace the ISC valve.

FI–82

EFI SYSTEM   –   Air Induction System (Idle Speed Control (ISC) Valve)

INSTALLATION OF ISC VALVE

(See Components on page 

FI–81

)

1. 

INSTALL ISC VALVE
(a) Install 

a 

new gasket and the ISC valve with the two nuts.

Torque: 18 N

⋅

m (185 kgf

⋅

cm, 13 ft

⋅

lbf)

(b)  Connect the following hoses to the ISC valve:

(1)  Water by–pass hose (from throttle valve)
(2)  Water by–pass hose (from water inlet housing)
(3)  Water by–pass hose (from EGR valve)

(c) (USA 

Spec.)

Install the vacuum pipe and water by–pass pipe (be-
tween ISC valve and EGR valve) to the air intake cham-
ber with the bolt.

(d)  (Exc. USA Spec.)

Install the water by–pass pipe (between ISC valve and
EGR valve) to the VSV (for fuel pressure control) with
the bolt.

(e)  Connect the ISC valve connector.

1. 

INSTALL LOWER HIGH–TENSION CORD COVER
(See steps 5 to 13 and 16 to 18 on pages 

FI–39

 to 41)

FI–83

EFI SYSTEM   –   Air Induction System (Idle Speed Control (ISC) Valve)