- Heater current for the air valve is supplied by the circuit opening relay power contact, the same circuit which feeds the fuel pump.
- Air valve operation can be quick checked by pinching off a supply hose and observing the rpm drop. When checked with a warm engine, the drop should be less than 50 rpm. When the engine is cold, the rpm drop should behigh.
Wax Type Air Valve
- The wax type air valve is integrated with the throttle body and varies an idle air by-pass opening as coolant temperature changes. The valve works on the principle of a spring loaded gate valve balanced against a coolant heated, wax filled thermo valve.
- When coolant temperature is cold, the wax filled thermo valve retracts allowing spring A to push the gate valve open. This allows air to flow from the air cleaner side of the valve to the intake side of the valve.
- A good quick check for the wax type air valve is to observe engine rpm throughout the warm up cycle. Look for high rpm upon initial startup and gradual reduction to normal curb idle speed as the engine reaches normal operatingtemperature.
- On D type EFI, the valve operation can also be checked by removing the air inlet pipe at the throttle body and blocking the fresh air port inside the throttle bore. When the engine is cold, engine rpm should drop greater than 100 rpm. Once the engine reaches normal operating temperature (~~ 176'F), rpm drop should not exceed 100rpm.
- As coolant temperature rises, the wax filled thermo valve expands allowing spring B to gradually close the valve (spring B is stronger than spring A). This causes engine rpm to decrease as air flow to the intake is decreased.
- The wax type air valve should be fully closed by the time engine coolant temperature reaches approximately 80'C (176'F).
- A large intake air chamber is provided to eliminate pulsation, thereby improving air distribution to each manifold runner. Long, narrow manifold runners are branched off to each intake port to improve air velocity at the intake valve. This design offers the following benefits:
• Fuel puddling is eliminated, providing for leaner cold engine and power air/fuel ratios. This equates to reductions in emissions and improved fueleconomy.
• Volumetric efficiency of the engine is improved, thereby improving engine torque andhorsepower.
Intake Air Chamber & Manifold
Port delivered Electronic Fuel Injection systems offer the advantage of not having to move fuel through the intake manifold. This allows for improved performance and emissions through optimum design of the intake air chamber and manifolds.
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Depending upon application, the intake air chamber and manifolds may be integrated or separate. Some Toyota engines utilize an ECU controlled variable induction system which optimizes manifold design for low and high speed engine operation. For more information on these systems, refer to "Other TCCS Related Systems."
- Air valve operation can be quick checked by pinching off a supply hose and observing the rpm drop. When checked with a warm engine, the drop should be less than 50 rpm. When the engine is cold, the rpm drop should behigh.
Wax Type Air Valve
- The wax type air valve is integrated with the throttle body and varies an idle air by-pass opening as coolant temperature changes. The valve works on the principle of a spring loaded gate valve balanced against a coolant heated, wax filled thermo valve.
- When coolant temperature is cold, the wax filled thermo valve retracts allowing spring A to push the gate valve open. This allows air to flow from the air cleaner side of the valve to the intake side of the valve.
- A good quick check for the wax type air valve is to observe engine rpm throughout the warm up cycle. Look for high rpm upon initial startup and gradual reduction to normal curb idle speed as the engine reaches normal operatingtemperature.
- On D type EFI, the valve operation can also be checked by removing the air inlet pipe at the throttle body and blocking the fresh air port inside the throttle bore. When the engine is cold, engine rpm should drop greater than 100 rpm. Once the engine reaches normal operating temperature (~~ 176'F), rpm drop should not exceed 100rpm.
- As coolant temperature rises, the wax filled thermo valve expands allowing spring B to gradually close the valve (spring B is stronger than spring A). This causes engine rpm to decrease as air flow to the intake is decreased.
- The wax type air valve should be fully closed by the time engine coolant temperature reaches approximately 80'C (176'F).
- A large intake air chamber is provided to eliminate pulsation, thereby improving air distribution to each manifold runner. Long, narrow manifold runners are branched off to each intake port to improve air velocity at the intake valve. This design offers the following benefits:
• Fuel puddling is eliminated, providing for leaner cold engine and power air/fuel ratios. This equates to reductions in emissions and improved fueleconomy.
• Volumetric efficiency of the engine is improved, thereby improving engine torque andhorsepower.
Intake Air Chamber & Manifold
Port delivered Electronic Fuel Injection systems offer the advantage of not having to move fuel through the intake manifold. This allows for improved performance and emissions through optimum design of the intake air chamber and manifolds.
-
Depending upon application, the intake air chamber and manifolds may be integrated or separate. Some Toyota engines utilize an ECU controlled variable induction system which optimizes manifold design for low and high speed engine operation. For more information on these systems, refer to "Other TCCS Related Systems."