Toyota Corolla 1988-1997 Repair Guide

Hot Air Intake (HAI) System



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

This system directs hot air to the carburetor in cold weather to improve driveability and to prevent carburetor icing. When the air temperature in the air cleaner is cold, the atmospheric port in the hot idle compensation (HIC) valve is closed, sending vacuum to the hot air intake (HAI) diaphragm. The HAI diaphragm moves, opening the air control valve which directs the heated air (from the exhaust manifold) into the air cleaner.

Once the air cleaner temperature is warm, the HIC valve atmospheric port is open. This keeps the air control valve closed, allowing the intake air to come directly down the air cleaner's snorkel from outside the car. This air is cooler than the air from around the exhaust manifold.


See Figures 1 and 2

  1. Remove the air cleaner cover and cool the HIC valve by blowing compressed air on it.
  3. Check that the air control valve closes the cool air passage.

Click image to see an enlarged view

Fig. Fig. 1: On a cold engine, the HIC valve should stayed closed

  1. Reinstall the air cleaner cover and warm up the engine.

Click image to see an enlarged view

Fig. Fig. 2: The valve will open as the engine warms up

  1. Check that the air control valve opens the cool air passage at idle.
  3. Visually check the hoses and connections for cracks, leaks or damage.