Lexus SC300 / Lexus SC400. Service manual - part 615

(d)  Connect the following hoses:

(1)  Air hose to ISC valve
(2) Air 

hose (from PS air control valve) to intake air con-

nector

4. 

CONNECT CONTROL CABLES TO THROTTLE BODY
Connect the following cables:

(1) Accelerator 

cable

(2)  A/T throttle control cable
(3)  (w/ Cruise Control System)

Cruise control actuator cable

5. 

INSTALL THROTTLE BODY COVER
Install the throttle body cover and hose clamp with the two
bolts and cap nut.

6.  CONNECT CABLE TO NEGATIVE TERMINAL OF

BATTERY

7. 

FILL WITH ENGINE COOLANT (See page 

CO–7

)

FI–79

EFI SYSTEM   –   Air Induction System (Throttle Body)

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)