Fault code P0506 – idle air control system RPM lower than expected

Fault code P0506 is called “Idle Air Control (IAC) System RPM Lower Than Expected” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0506

OBD-II Trouble Code P0506 is defined as “Idling Acceleration Control (IAC) RPM below expected”. Set when the Powertrain Control Module (PCM) is unable to maintain or control engine speed at idle.

Fault code P0506 – idle air control system RPM lower than expected

In most cases, the PCM will attempt to make adjustments to various systems such as fuel adjustment, ignition angle, injection pulse width, and others. Trying to maintain the idle speed set point. However, when this limit is reached, the PCM will set code P0506 and turn on the warning lamp.

The idle speed in gasoline engines is regulated and controlled by the idle speed control valve, which is usually located on the throttle body. The valve is driven by a stepper motor, which receives commands from the PCM based on information received from various sensors located on the engine.

As long as the throttle remains closed, speed and idle quality are controlled by the PCM through the idle control valve.

For example, if the engine is started in sub-zero temperatures, the PCM commands the valve to allow less air to enter the engine. This enriches the fuel-air mixture and creates conditions for cold-weather idle control.

As the engine warms up and combustion becomes lighter and more complete. The PCM commands the idle control valve to increase the amount of air flowing into the engine according to changing conditions.

If the load on the engine changes, such as when some electrical consumers are turned on or off. The PCM adapts the signal voltage to the idle control valve. To ensure that the idle speed remains stable, and at the rpm level specified by the manufacturer.

Note that the idle air control valve is closed by the PCM when the throttle is opened. This is done to prevent excess air from entering the engine.

Symptoms of vehicle malfunctions

The main signal that an error P0506 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check Engine” control lamp on the control panel will light up (the code will be recorded in the memory as a malfunction).
  2. Floating revolutions, as well as attempts to stall at idling speed.
  3. Idle speed is higher or lower than normal.
  4. The engine may stall if the idle speed is not maintained by pressing the accelerator pedal.

Depending on the symptoms, the severity of code P0506 can range from moderate to severe. Therefore, it is recommended that the problem be corrected as soon as possible.

Factors that can cause this error code

The error code P0506 can mean that one or more of the following problems have occurred:

  • The idle speed control valve is defective.
  • The idle stroke control valve (IAC) connector is damaged.
  • Damaged, burned, shorted, or corroded wiring.
  • Defective stepper motor.
  • Vacuum leakage in motor.
  • Sometimes faulty PCM is the cause.

How to fix or reset OBD-2 code P0506

Some suggested steps for troubleshooting and fix the error code P0506:

  1. Read all data and stored error codes, using an OBD-II scan tool.
  2. Clear the codes and check if error code P0506 appears again.
  3. Monitor the engine at idle, with the gear engaged and disengaged. To check if the engine idle speed matches the values specified in the manufacturer’s technical documentation.
  4. Check the engine for vacuum leakage.
  5. Inspect the throttle for carbon buildup. Also, at the body and inlet of the idle air control valve.
  6. Disconnect and inspect the idle air intake control valve.
  7. Check that the passages of the idle air control valve are not clogged.

Diagnose and repair of problems

Connect a scan tool and read and write down all available codes. This information may be useful if an intermittent fault is later diagnosed.

If there are other codes present along with code P0506, diagnose and repair them in the order in which they have been stored. The most likely additional codes are usually related to the vacuum system.

Therefore, check the vacuum system for leaks caused by damaged vacuum lines. If necessary, repair and remove any codes before operating the vehicle. Then, retest the system to see if any codes return.

Throttle valve

If the code does not disappear, remove the throttle body from the intake manifold and check it for excessive carbon buildup. In some cases, it is possible to remove light carbon deposits from the throttle body and auxiliary air passages using approved cleaners.

However, heavy deposits usually cannot be removed without damaging the throttle body or idle control valve. In these cases, the best option is to replace the throttle body or idle control valve with genuine parts.

When installing cleaned or replacement parts, make sure that all seals and gaskets are also replaced to prevent vacuum leakage. Double check all vacuum line connections before starting the engine or operating the vehicle.

Checking the wires and connections

If code P0506 has not disappeared, perform a thorough visual inspection of all related wiring. Look for damaged, burned, shorted, or corroded wires and connectors.

After no visible damage is found, check the resistance, ground, and reference voltages. Compare all readings with those in the manual. If necessary, replace the wiring to make sure all readings are in accordance with the manufacturer’s specifications.

Stepper motor and idle valve

Check the actual signal voltage reaching the stepper motor at the connector. Use the scan tool to command the idle control valve to open. Compare the value obtained with the values indicated in the manual.

Special diagnostic programs usually give a voltage range, which corresponds to the degrees of idle valve opening. And sometimes the degrees of rotation of the stepper motor.

These readings must correspond exactly to the declared values, otherwise the harness must be replaced. If all the readings obtained agree with the stated values, the stepper motor is defective and must be replaced.

These actions should solve the problem with the error P0506. But if it still appears again, then probably the problem is recurring. In this case diagnosing can be a difficult task. And sometimes it is necessary to let the problem get worse in order to understand exactly where the problem is.

On which vehicles does this problem occur most frequently

Fault code P0506 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (A4, Q5)
  • Chevrolet (Colorado, TrailBlazer)
  • Dodge (Caravan)
  • Ford (Explorer, F-150, Focus)
  • GMC (Envoy)
  • Honda
  • Hyundai
  • Mazda (3, 6, CX-7)
  • Nissan (Altima)
  • Skoda (Octavia)
  • Subaru (Outback)
  • Volkswagen
  • GAZelle (ZMZ 405)
  • LADA (Kalina, Niva, Priora)
  • UAZ (Patriot)
  • VAZ (2112, 2114, 2115)

Fault code P0506 can sometimes be found with other errors. The most common are the following: P0171, P0174, P0351, P0356, P0505, P0507, P1400.


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