Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Throttle Opener Control System


See Figure 1

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Fig. Fig. 1: Throttle opener control system

The Throttle Opener Control System (TOCS) is used on E-series engines. The purpose of the system is to reduce hydrocarbon emissions during coasting conditions.


High manifold vacuum during coasting prevents the complete combustion of the air/fuel mixture because of the reduced amount of air. This condition will result in a large amount of HC emission. Leaning the air/fuel mixture for a short time (during the high vacuum condition) will reduce the emission of the HC. However, changing the air/fuel mixture with the mixture adjusting screw will cause poor engine idle and increase emissions during normal idle conditions.

The TOC system consists of a servo diaphragm, vacuum control valve, throttle opener solenoid valve, speed detecting switch and amplifier on manual transaxle models. Automatic transaxle models use an inhibitor and inhibitor relay in place of the speed detecting switch and amplifier. At the moment when the manifold vacuum increases, as during deceleration, the vacuum control valve opens to transfer the manifold vacuum to the servo diaphragm chamber and the carburetor throttle valve opens slightly. Under this condition, the proper amount of fresh air is sucked into the combustion chamber. As a result, a more complete ignition takes place, burning much of the HC in the exhaust gases.


When the engine is idling too high and does not drop to idling speed, the TOC system should be checked.

  1. Check for continuity between the green/red and black terminals of the function check connector with the ignition OFF . If no continuity exists, the solenoid may be at fault. Replace the valve assembly.
  3. Manual transaxle vehicles: remove the speedometer cable and spin the speedometer in the combination meter to confirm that the pointer indicates more than 10 mph (16 km/h). The voltage at the function check connector green/red and black terminals should read 0 volts above 10 mph (16 km/h) and 12 volts below 10 mph (16 km/h). If not the amplifier or speed detecting switch may be at fault.
  5. Automatic transaxle vehicles: voltage at the function check connector terminals should be 12 volts in Neutral or Park and 0 volts in all other positions. See Step 2.
  7. Disconnect the harness at the solenoid. Tee a vacuum gauge into the vacuum hose going to the opener servo diaphragm.
  9. Warm the engine and run to 3000-3500 rpm then quickly close the throttle. At this time, the vacuum should increase to 23.6 in. Hg or above and then decrease to the level set at idling. If not the temperature control valve may be at fault.
  11. If the pressure is not correct, lower the level by turning the adjusting screw or not in the clockwise direction. If it is the higher, turn the screw counterclockwise.
  13. Adjusting servo stroke: connect a tachometer and warm the engine. Disconnect the rubber hose between the diaphragm and control valve. Connect the hose to the intake manifold. If the engine speed goes to 1650-1850 rpm, the servo is working properly. Adjust the engine speed until it is in range using the diaphragm adjusting screw on the link lever.