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Honda OBD II Specific Codes

P0505 – Idle Air Control Valve Malfunction (Honda)

If your Accord or Civic has a P0505 code, there are three likely causes:

  1. The IACV-AAC valve harness is open and allowing moisture inside
  2. The IACV has a poor electrical connection, or
  3. The idle air control valve itself is faulty

Other Honda models that can sometimes have this issue include the Odyssey minivan and the Honda Pilot, both of which have technical service bulletins (TBBs) listed for them that any repair shop can access for more details.

For the driver, a P0505 code will usually mean that the engine becomes hard to start, runs roughly, or idles erratically. The engine may also shut off (choke out or stall) at stop lights after being driven to temperature (e.g. only after the vehicle has “warmed up”).

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The IACV controls the engine’s idle speed at a specific level. When the engine is cold, the car will idle at a higher speed so that the engine can warm up as quickly as possible. This way, emissions control systems can reach optimum operating temperatures as fast as possible. The IACV manipulates the idle speed by controlling the amount of auxiliary air that enters the engine from the bypass passage…more air means faster idle.

If the IACV isn’t working correctly, the engine can be starved of oxygen…this causes the symptoms (rough idle, stalling, etc.) described above. Often times a short-circuit is the cause of an IACV problem, so it’s a good idea to check the wiring harness first when diagnosing the problem.

Occasionally, the valve itself may be blocked or stuck and require replacement. Whatever the issue, a simple diagnostic of the wiring harness and circuit is usually all that’s required to locate the problem.

Author Jason Lancaster is the editor of AccurateAutoAdvice.com as well as a blogger for HondaPartsOnline.net. When Jason isn’t writing about idle air control valves (or some other automotive topic), he’s watching NBA hoops or spending time with his family.

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6 thoughts on “P0505 – Idle Air Control Valve Malfunction (Honda)”

  • Michael Johnson

    July 18, 2021 at 7:25 pm Reply

    Verify temp sensor (ETC) is reading correct. ECM uses it to regulate idle. Also use no spill funnel to verify there is not an air bubble in the coolant system. This can cause the ECT to give false readings to ECM.

  • Tito

    May 10, 2020 at 5:30 pm Reply

    Hi Eric, I’m stumped I’ve gone through 2 iacv’s already and still throws the code and idles at about 1500 rpm and doesn’t go down it starts up fine but when it starts to warm up the problem comes back, I’m lost.

    • Tito

      May 10, 2020 at 5:32 pm Reply

      Also I give it gas gas and it starts bucking/jerking like air is being cut out, when I disconnect the iacv the idle goes down but the bucking/jerking is still there when I give it gas, any suggestions?

      • Owen Deleskie

        January 4, 2021 at 7:04 pm Reply

        Hey Tito I know it might be a long shot, but I’m having exactly the same issue with the iacv, did you end up figuring it out ? I’m in the exact same senario

        • Teg

          June 6, 2022 at 4:58 pm Reply

          Has anyone figured this out?Please any information is helpful my car is showing the same exact symptoms

    • Flávio Carvalho

      October 16, 2020 at 11:43 am Reply

      Olá
      estou com esse exato problema.
      já troquei a iacv e verifiquei a fiação
      preciso de ajuda.

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