Toyota Corolla 1988-1997 Repair Guide

Hot Idle Compensation (HIC) System

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OPERATION



See Figure 1

This system is used on the 4A-F engines only.



Click image to see an enlarged view

Fig. Fig. 1: The components of the Hot Idle Compensation (HIC) system are located on the air cleaner

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 Figure 2

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



Click image to see an enlarged view

Fig. Fig. 2: Test for air flowing from the HAI diaphragm side to the carburetor side with the port of the valve closed

  1. Check that air does not flow from the carburetor side to the HAI diaphragm side with the atmospheric port open.
  2.  
  3. Check that air does NOT flow from the HAI diaphragm side to the atmosphere port while closing the carburetor side below this temperature 72°F (22°C). Using a hotwater bath, heat the HIC valve to above 84°F (29°C).
  4.  

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.  

 
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