Idle speed control valve testing

The idle speed control valve controls the amount of air allowed to bypass the throttle to increase or decrease idle speed. Whenever the idle position switch is closed, the valve is in operation.

• Listen and feel for valve vibration or humming.

• If valve is not operating, check that idle switch is operating correctly as described above.

• If valve is functioning but idle speed is erratic, check valve as described below.

Remove two hoses (A) and electrical harness connector (C) from valve. Remove mounting nuts (B). Remove idle speed control valve.

• Check valve piston for free movement by moving/shaking removed valve abruptly. Piston should slide freely.

• Test resistance values in valve electrical components. Compare to specifications below.

• If no faults are found, reinstall valve and reconnect wiring harness connector.

Idle Speed Control Valve Resistance

• Between outer terminals 40 £2

• Between center terminal and each outer terminal 20 £2

— Start engine and allow it to reach operating temperature.

Then turn off engine and all electrical accessories.

• Remove top hose from valve so that piston can be seen.

• Turn ignition on. Valve piston should move approximately halfway across valve opening.

^ If idle speed is not within specifications and no faults are detected with idle speed control valve, or if valve piston did not move correct distance in previous test, test signal from


• With ignition off, disconnect electrical harness connector from idle valve.

• With ignition on, there should be battery voltage at terminal 4 (center terminal).

• If voltage is not present, test ECM harness inputs/outputs as described later.

Porsche 964 Idle Speed Control Valve

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