How do I adjust the throttle opener if engine speed does not drop to idle?

Turn the adjusting screw counterclockwise so throttle opener operating pressure is on the high vacuum side, 3.3 kPa (25 mmHg, 0.98 inHg) above the specified value, then turn the adjusting screw 1/4 of a turn clockwise so the operating pressure drops by 3.3 kPa (25 mmHg, 0.98 inHg).

What if the throttle opener operating pressure cannot be observed clearly?

Turn the adjusting screw counterclockwise so the operating pressure is on the high vacuum side 6.7 kPa (50 mmHg, 1.97 inHg) above the mid-point of the specified range, then turn the adjusting screw 1/2 of a turn clockwise.

What is the altitude range covered by the operating pressure chart?

The chart (SEC259A) covers altitudes from 0 to 6,000 ft (0 to 2 km), correlating operating pressure with atmospheric pressure.

What range of atmospheric pressure does the chart show?

The atmospheric pressure scale spans 66.7 kPa (500 mmHg) up to 100.0 kPa (750 mmHg), or roughly 20 to 30 inHg.

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Nissan T.O.C.S. Throttle Opener Adjustment & Altitude Chart - EF & EC-31

T.O.C.S. operating-pressure vs altitude chart and adjustment steps, Nissan EF & EC manual

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TOCS adjustment page with operating-pressure-versus-altitude graph; turn adjusting screw in 3.3 kPa (25 mmHg, 0.98 inHg) increments to set decel throttle-opener pressure.

AI caption June 2005 · Photo 131 of 412

This is a page from a Nissan factory service manual, section EF & EC (Engine Fuel & Emission Control), page EF & EC-31, covering the Exhaust Emission Control — Throttle Opener Control System (T.O.C.S.), continuing an Inspection and Adjustment procedure. Steps 8–10 describe how to adjust the throttle opener operating pressure: racing the engine to check adjustment, and if engine speed does not drop to idle, turning the adjusting screw counterclockwise so the operating pressure is 3.3 kPa (25 mmHg, 0.98 inHg) above the specified value on the high vacuum side, then turning it 1/4 turn clockwise to drop pressure by the same amount. If the operating pressure cannot be observed clearly, the screw is set 6.7 kPa (50 mmHg, 1.97 inHg) above the mid-point of the specified range, then turned 1/2 turn clockwise. A note states the operating pressure should be correctly set within the specified range after these adjustments even if engine speed cannot be decreased to idling. The lower portion of the page is a nomograph (figure SEC259A) correlating throttle opener operating pressure (40.0–80.0 kPa / 300–600 mmHg) with atmospheric pressure (66.7–100.0 kPa) and altitude (0–6,000 ft / 0–2 km), with reference lines labeled "A" and "B" for altitude compensation of the specification.

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Frequently asked questions

How do I adjust the throttle opener if engine speed does not drop to idle?: Turn the adjusting screw counterclockwise so throttle opener operating pressure is on the high vacuum side, 3.3 kPa (25 mmHg, 0.98 inHg) above the specified value, then turn the adjusting screw 1/4 of a turn clockwise so the operating pressure drops by 3.3 kPa (25 mmHg, 0.98 inHg).
What if the throttle opener operating pressure cannot be observed clearly?: Turn the adjusting screw counterclockwise so the operating pressure is on the high vacuum side 6.7 kPa (50 mmHg, 1.97 inHg) above the mid-point of the specified range, then turn the adjusting screw 1/2 of a turn clockwise.
Does the throttle opener pressure need to be in spec even if the engine won't return to idle?: Yes. The document states the throttle opener operating pressure should be correctly set within the specified range after the adjustments, even if the engine speed cannot be decreased to idling.
What is the altitude range covered by the operating pressure chart?: The chart (SEC259A) covers altitudes from 0 to 6,000 ft (0 to 2 km), correlating operating pressure with atmospheric pressure.
What range of atmospheric pressure does the chart show?: The atmospheric pressure scale spans 66.7 kPa (500 mmHg) up to 100.0 kPa (750 mmHg), or roughly 20 to 30 inHg.