Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSHONDA2005CIVIC L4-1.7L CNGREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONIDLE CONTROL SYSTEM
2005 Honda Civic L4-1.7L CNG
Idle Control System
2005 Honda Civic L4-1.7L CNGSECTION Idle Control System
Idle Control System
When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the power steering load is high, or the alternator is charging, the PCM controls current to the idle air control (IAC) valve to maintain the correct idle speed. Refer to the System Diagram to see the functional layout of the system.
Brake Pedal Position Switch
The brake pedal position switch signals the PCM when the brake pedal is pressed.
Idle Air Control (IAC) Valve
To maintain the proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the PCM.
Power Steering Pressure (PSP) Switch
The PSP switch signals the PCM when the power steering load is high.
Idle Control System Diagram
The idle speed of the engine is controlled by the idle air control (IAC) valve:
- After the engine starts, the IAC valve opens for a certain amount of time. The amount of air is increased to raise the idle speed.
- When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to engine coolant temperature.
When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the power steering load is high, or the alternator is charging, the PCM controls current to the idle air control (IAC) valve to maintain the correct idle speed. Refer to the System Diagram to see the functional layout of the system.
Brake Pedal Position Switch
The brake pedal position switch signals the PCM when the brake pedal is pressed.
Idle Air Control (IAC) Valve
To maintain the proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the PCM.
Power Steering Pressure (PSP) Switch
The PSP switch signals the PCM when the power steering load is high.
Idle Control System Diagram
The idle speed of the engine is controlled by the idle air control (IAC) valve:
- After the engine starts, the IAC valve opens for a certain amount of time. The amount of air is increased to raise the idle speed.
- When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to engine coolant temperature.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.