Toyota Tercel 1984-1994 Repair Guide

Hot Idle Compensation

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OPERATION



Used on 3A-C and 3E engines.

The hot idle compensation (HIC) system allows additional air to enter the intake manifold, maintaining a proper air/fuel mixture during idle at high temperatures. It also controls the vacuum supplied to the HAI valve, allowing heated air to enter the air cleaner during cold operation.

TESTING



See Figures 1, 2, 3 and 4

  1. Check that air flows from the HAI diaphragm side to the carburetor side while closing the atmospheric port.
  2.  
  3. Check that air does not flow from the carburetor side to the HAI diaphragm side with the atmospheric port open.
  4.  
  5. Check that air does NOT flow from the HAI diaphragm side to the atmosphere port while closing the carburetor side below these temperatures:
    1. 72°F (22°C) - 3A-C engines
    2.  
    3. 79°F (26°C) - 3E engines
    4.  

  6.  
  7. Using a water bath, heat the HIC valve to above 84°F (29°C) on 3A-C engines or 93°F (34°C) on 3E engines.
  8.  

Do not allow water to get inside the valve.

  1. Check that air flows from the HAI diaphragm side to the atmospheric port while closing the carburetor side.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: With the atmospheric port closed, air should flow from the HAI diaphragm to the carburetor



Click image to see an enlarged view

Fig. Fig. 2: Air should not flow from the carburetor to the HAI diaphragm with the atmospheric port open



Click image to see an enlarged view

Fig. Fig. 3: When below its calibrated temperature, air should not flow from the HAI diaphragm to the atmospheric port with the carburetor side closed



Click image to see an enlarged view

Fig. Fig. 4: When above its calibrated temperature, air should flow from the HAI diaphragm to the atmospheric port with the carburetor side closed

 
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