Technical Service Bulletin Unstable Idle 80-81 911SC

Subject: Unstable Idle Speed  Models: 1980-81 911SC

At lower ambient temperatures, engine idle speed can be unstable due to adjustment


To Correct:

-Adjust ignition timing at operating temperature to 5°BTDC (vacuum hose disconnected).

-Adjust idle RPM at operating temperature to 850 RPM.

-Adjust CO at idle to 0.6 ± 0.2%.


To avoid measuring errors, do not use ignition timing light with timing advance feature.

If above procedure does not stabilize idle speed:

-Remove deceleration valve

-Using a suitable socket, compress valve by 1 mm as shown.

-Reinstall the valve

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