Toyota Pick-ups/Land Cruiser/4Runner 1989-1996

Hot Air Intake (HAI) System



See Figures 1, 2 and 3

This system only applies to the 22R engine.

This system allows hot air from around the exhaust manifold to be routed to the carburetor in cold weather. Instead of cold air being sucked into the air cleaner all the time, a thermo-valve in the air cleaner housing closes when the temperature inside the air cleaner falls below a certain point. When the thermo valve is closed, a diaphragm on the air cleaner neck is activated and it opens the air control valve. This not only prevents cold outside air from entering the air cleaner, but allows the hotter air from around the exhaust manifold to flow in. This system improves driveability by maintaining a constant air intake temperature, resulting in more stable fuel atomization. It also serves to prevent carburetor icing in cold and moist weather.

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Fig. Fig. 1: The HAI system has two main companants, the thermo valve and the diaphragm

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Fig. Fig. 2: The thermo valve controls air flow according to the ambiant tempreture

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Fig. Fig. 3: HAI system operating conditions


  1. Visually inspect all hoses and connections for cracks, leaks or other damage.
  3. Remove the air cleaner top.
  5. Cool the thermo valve by blowing compressed air on it.
  7. With the engine idling and the thermo valve closed (cool), check to see if the air control valve in the neck of the air cleaner is open and allowing hot air to enter the air cleaner.
  9. Install the top of the air cleaner and run the engine until it reaches normal operating temperature.
  11. Check that the air control valve is now closed and only cool air is being allowed to enter the air cleaner.