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All codes/P0505

P0505

Idle Control System Malfunction

Moderate severity

This code means your car's computer has detected a problem with the system that controls your engine's idle speed. This system ensures your engine runs smoothly when your foot isn't on the gas pedal.

Idle Control System Malfunction

Common causes

  • Faulty Idle Air Control (IAC) Valve

    The IAC valve can become clogged with carbon or fail electronically, preventing it from regulating idle speed.

    high

    Typical part cost: $50-200 part

  • Vacuum Leaks

    Leaking vacuum hoses, intake manifold gaskets, or PCV system components can introduce unmetered air, disrupting idle.

    medium

    Typical part cost: $0-100 for repair

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First things to check

  1. 1Inspect the IAC valve and throttle body for carbon buildup and clean if necessary.
  2. 2Check all vacuum lines and intake manifold gaskets for leaks using a smoke machine or by listening for hissing sounds.

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Tools you may need

Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.

Illustration of a Bluetooth OBD2 adapter, not a product photo

Basic checks

Veepeak OBDCheck BLE

A Bluetooth LE adapter for reading standard engine codes and supported live data.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Regular diagnostics

vgate iCar Pro BLE 4.0

A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Another option

OBDLink CX

A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.

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Illustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.

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Related codes

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Frequently asked questions

What is an IAC valve?

The Idle Air Control (IAC) valve is an electronically controlled valve that regulates the amount of air bypassing the closed throttle plate, thereby controlling the engine's idle speed.

Can a P0505 code cause my car to stall?

Yes, a malfunctioning idle control system, often due to a faulty IAC valve or vacuum leak, can lead to an unstable idle speed, causing the engine to stall, especially when you come to a stop.

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