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Common Symptoms of a Faulty Idle Air Control Valve

By R&D
Published on January 20th, 2025

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The Idle Air Control (IAC) Valve is a crucial component of the engine management system. It is typically positioned near the throttle body and is responsible for regulating the amount of air that bypasses the throttle plate during idle.

This control is essential for maintaining a stable engine idle speed, preventing stalling, and ensuring smooth transitions between idle and acceleration. The IAC Valve is comprised of a stepper motor that drives a valve stem to control the opening and closing of an air bypass passage.

The stepper motor receives signals from the Engine Control Module (ECM)and adjusts the valve stem's position, thereby controlling the amount of air that enters the engine. If the IAC Valve malfunctions, it can lead to a variety of engine problems. These issues may include erratic idle, stalling, difficulty starting, or excessive fuel consumption. A faulty IAC Valve can also contribute to increased emissions and reduced overall engine performance.

Common Symptoms of a Faulty Idle Air Control Valve

This article highlights the typical symptoms of a faulty IAC Valve, to help you identify potential issues and their root causes.

What Causes Idle Air Control Valve Failures?

Contamination and Clogging: Contaminants and carbon deposits can accumulate within the IAC Valve chamber due to the continuous flow of air. These deposits can obstruct or completely block the valve's passageways, leading to internal damage, jamming, or clogging. This can result in a malfunctioning valve, often caused by low-quality fuel or inadequate maintenance.

Electrical Problems: A poor electrical connection, especially in older vehicles, can contribute to IAC Valve malfunctions. Loose or corroded connectors, as well as short circuits, can also affect the valve's proper operation.

Worn or Damaged Internal Components: Over time, the internal components of the IAC Valve can wear out or become damaged due to normal use or excessive heat. This can lead to reduced valve performance or complete failure.

Common Symptoms of the Faulty Idle Air Control Valve

Malfunction Indicator Light (MIL) or Check Engine Light (CEL) Illuminates

A malfunctioning IAC Valve may trigger the vehicle's On-Board Diagnostic (OBD) system to illuminate the MIL and store a corresponding Diagnostic Trouble Code (DTC) in its memory. However, the MIL can be illuminated for multiple reasons, so using a Scan Tool to diagnose the specific issue is essential.

Engine Stalling

The principal function of the IAC Valve is to maintain the correct amount of airflow to the engine at idle. If the valve fails to open properly, the engine may not receive the necessary air to keep running, leading to stalling. This can be particularly dangerous in traffic or at intersections, where sudden stalling can increase the risk of accidents.

Rough Idling

A faulty IAC Valve can also cause rough idling, where the engine runs unevenly or shakes while idling. This occurs because the valve is not regulating the air flow correctly, causing fluctuations in the engine’s idle speed. You might notice the engine RPMs fluctuating or dropping unexpectedly. Over time, rough idling can lead to increased engine wear and may also affect the overall driving experience, making it less smooth and more uncomfortable.

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Identify a Faulty Idle Air Control Valve with the Innova Scan Tool

The Innova Scan Tool quickly retrieves and identifies existing DTCs in your vehicle’s computers. With a quick OBD2 Scan, you can retrieve existing DTCs, the I/M Status of the vehicle, and any collected Freeze Frame data from these computers. Refer to the Innova Coverage Checker to determine the level of information supported on your vehicle by year, make, and model. The Innova Scan tool effectively diagnoses IAC Valve-related issues, helping you easily pinpoint and resolve problems.

Additionally, the Innova Scan Tool lets you view Live Data PIDs and presents OEM Enhanced Live Data, with advanced information for complete vehicular diagnostics. You can also read the IAC Sensor Voltage Input value to determine if the IAC Sensor Voltage Input value matches with the actual IAC sensor voltage or if it changes after many movements. The normal operating value of the IAC sensor depends on your vehicle.