Toyota Tercel 1984-1994 Repair Guide

Throttle Positioner

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OPERATION



Used on 3A-C and 3E engines.

To reduce HC and CO emissions, the throttle positioner (TP) opens the throttle valve to slightly more than the idle position when decelerating. This keeps the air/fuel ratio from becoming excessively rich when the throttle valve is quickly closed. In addition, the TP is used to increase idle rpm when power steering fluid pressure exceeds a calibrated value and/or when a large electrical load is placed on the electrical system (headlights, rear defogger etc).

TESTING



Vacuum Transmitting Valve

See Figure 1

  1. Check that air flows without resistance from B to A .
  2.  
  3. Check that air flows with difficulty from A to B .
  4.  
  5. If a problem is found, replace the vacuum delay valve.
  6.  

When replacing the vacuum transmitting valve, side A should face the throttle positioner.

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Fig. Fig. 1: VTV airflow

Vacuum Switching Valve

See Figures 2, 3, 4 and 5

Used on 3E engines.

  1. The vacuum switching circuit is checked by blowing air into the pipe under the following conditions:
    1. Connect the vacuum switching valve terminals to battery voltage.
    2.  
    3. Blow into the tube and check that the VSV switch is open.
    4.  
    5. Remove battery voltage from the terminals.
    6.  
    7. Blow into the tube and check that the VSV switch is closed (no flow).
    8.  

  2.  
  3. Check for a short circuit within the valve. Using an ohmmeter, check that there is no continuity between the positive terminal and the VSV body. If there is continuity, replace the VSV.
  4.  
  5. Check for an open circuit. Using an ohmmeter, measure the resistance (ohms) between the two terminals of the valve. The resistance should be 38-44- at 68°F (20°C). If the resistance is not within specifications, replace the VSV.
  6.  

The resistance will vary slightly with temperature. It will decrease in cooler temperatures and increase with heat, slight variations due to temperature range are not necessarily a sign of a failed valve.

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Fig. Fig. 2: The VSV should be open with battery voltage applied to the terminals



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Fig. Fig. 3: The valve should be closed when the voltage is removed



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Fig. Fig. 4: Checking the valve for a short circuit



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Fig. Fig. 5: Checking the VSV for an open circuit

Throttle Positioner Diaphragm

See Figures 6 and 7

Check that the linkage moves in accordance with applied vacuum.



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Fig. Fig. 6: Throttle positioner linkage movement on 3A-C engines



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Fig. Fig. 7: Linkage movement on 3E engines

Jet

See Figure 8

Used on 3E engines.

Check the jet by blowing air through both sides. Air should pass freely both ways.



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Fig. Fig. 8: Airflow through the jet should not be blocked in either direction

 
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