Listen for clicking sound after engine is shut off. If no sound is heard, check ISC valve and wiring.
To check wiring circuit, turn engine off. Unplug ISC valve connector. Turn ignition on with engine off. Connect voltmeter between B1 and B2 terminals of wiring harness connector. See Fig 1. Battery voltage should be present. If not, check wiring between ISC valve and EFI main relay.

To check ISC valve, turn ignition off. Unplug ISC valve connector. Measure resistance between ISC valve terminals. See Fig 1. See ISC VALVE RESISTANCE SPECIFICATIONS table. Replace ISC valve if resistance is not as specified.

ISC VALVE RESISTANCE SPECIFICATIONS

Terminals	Ohms
B1 to S1 or S3	10-30
B2 to S2 or S	10-30

NOTE: Before removing ISC valve, drain coolant from cooling system. Remove both coolant by-pass hoses.

To check valve operation, remove ISC valve from vehicle. Apply battery voltage to terminal B1 and terminal B2. See Fig 1. Repeatedly ground terminals S1, S2, S3 and S in sequence. Valve should close. Remove ground wires.
Apply battery voltage to terminals B1 and B2. Repeatedly ground terminals S, S3, S2 and S1 in sequence. Valve should move toward open position. Replace valve if operation is not as specified.

Fig 1: Checking ISC Valve

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Idle Speed Control (ISC) System

Use the Manual With the Right Hardware

When to See a Mechanic