Air intake device (Honda Accord 3)

The electronic fuel injection system consists of three units: air intake, electronic control, fuel supply.

This device supplies air to all engine components. It consists of an air filter, an air intake pipe, a throttle body, an idle control unit, an accelerated idle mechanism, and an air intake manifold. A resonator built into the air intake pipe reduces the noise from the air sucked into the pipe.

Throttle body

The throttle body contains two auxiliary channels and one main channel in the center. To prevent icing of the throttle valves and channel walls under certain weather conditions, the lower part of the body is heated with coolant. A sensor is attached to the primary valve to monitor changes in the throttle opening width. An air buffer is used to slow the throttle as it approaches the closed position.

Engine Idle Speed Control

The correct air/fuel mixture ratio during idle is controlled by the on-board computer using electromagnetic valves such as the idle air control valve, high idle speed control valve, and air conditioning idle control valve. All of these valves, except the last one, change the air flow through the air intake manifold. The air conditioning control valve opens the throttle valve when the ECU switches on the air conditioning via electrical signals.

The purpose of the idle speed control valve is to compensate for the decrease in idle speed caused by electrical and other loads on the engine. This is achieved by the valve letting additional air into the air intake manifold at the right moment. Due to the increased air flow, the engine shaft speed increases to the set value of 750±50 rpm. The response time of the valve depends on the magnitude of the voltage change at the FR terminal of the generator. The valve also begins to gradually reduce the shaft speed of the warming-up engine as soon as the coolant temperature reaches 55°C. To prevent unstable engine operation immediately after the first strokes, the valve is set open when the starter is engaged and for a short time after starting to ensure that a sufficient amount of air is supplied to the air intake manifold. The high idle speed control valve prevents unstable engine operation during its warm-up, when the idle speed should be higher. This valve also allows additional air to enter the air intake manifold when the atmospheric pressure falls below 660 mm Hg.



The idle speed control solenoid valve maintains the idle speed within 750±50 rpm when the air conditioner is on. The valve acts on the idle speed control diaphragm, which opens the throttle valve to increase the idle speed. The valve also remains open at low coolant temperatures (immediately after starting), thus ensuring stable idle speed regardless of the position of the air conditioner switch.

Idle speed control (bypass circuit)

The fuel supply is cut off at a certain position or angle of the throttle valve. If the position of this valve is changed to adjust the idle speed, the position or angle of the cutoff also changes and the device may stop cutting off the fuel supply at the right time. To solve this problem, an adjustment bypass channel is installed in the throttle body. This channel allows you to change the air flow passing through the throttle valve into the air intake manifold without changing the position of the throttle itself.

However, idle speed usually does not require adjustment.

High Idle Speed Control Mechanism

To prevent the engine from running erratically while it is warming up, it is necessary to set it to a higher idle speed. The bypass valve is controlled by a plunger with a thermocouple. When the thermocouple is cold, the valve is open. When the thermocouple heats up, the valve closes. Therefore, when the engine, and therefore the thermocouple, is cold, additional air enters the air intake manifold, and the engine runs faster than usual. When the engine temperature starts to reach the operating value, the valve starts to close, reducing the additional air flow.