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Idle Control Unit Guides

How to Fix a Faulty Idle Air Control Unit

The idle air control (IAC) unit is a motor controlled by your car's onboard computer that regulates the idle speed of the engine. So when the engine starts to idle roughly or stalls often, it could be traced to a faulty IAC unit. In many cases, problems with the idle air control unit can be traced to dirt or carbon buildup around the motor's moving parts that need to be cleaned. In this guide, we will show you how to locate your broken IAC unit in your car and how you can fix it back to shape.

Difficulty level: Moderate

What you'll need:

  • Screwdriver
  • Socket and ratcher set
  • Choke/carburetor cleaner
  • Cleaning rag
  • Wrench
  • OBD/OBD II scanner

Step 1: Check if the engine light is on. If it is, use an OBD or OBD II diagnostic scanner to retrieve the codes. A malfunctioning IAC unit will display a specific code depending on the make of the vehicle. Check the maintenance manual of your car for the respective OBD code for your vehicle's IAC unit.

Step 2: If the scanner confirms that the idle air control unit is the source of the problem, open the hood and locate and disconnect the unit. In most cars, the IAC unit is mounted on top of the engine next to the throttle body. The unit is either secured by four bolts or screws, so use a screwdriver or a wrench to free it from the engine.

Step 3: Disconnect the wire assembly connected to the unit. IAC units are usually connected to three wires: one for the current, one for the ground, and the other that leads to the computer. Disconnect each one carefully and mark with a felt pen to ensure proper assembly later.

Step 4: Once the bolts and wires have been removed, pull the unit away from the engine. In some models, you may also need to disconnect the air cleaner hose connected to the throttle body.

Step 5: Spray the IAC unit with choke or carburetor cleaner. Use a cleaning rag to wipe off any buildup in the unit. You can the motor's spindle back and forth to access those hard-to-reach areas around it. We also recommend cleaning the throttle body while the unit is disconnected.

Step 6: After cleaning the IAC unit, reattach it to the engine. Make sure that the motor's pintle fits into the space in the throttle body and that the wires are attached to their proper terminals. If you have disconnected the air cleaner hose, reconnect that as well.

Step 7: Switch on the ignition and let the engine run idle for several minutes. The engine should run smoothly without any sputtering or stalling. But if the problems persist, the idle air control unit may need to be replaced.

Note: Make sure that the engine is switched off and the negative battery cables disconnected before starting. Handling the idle air control unit, especially when disconnecting the wires, while power is running through the system may lead to electric shock and damage to the component.

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