P0505 OBD-II Trouble Code: Idle Control System Malfunction

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Cost of diagnosing the P0505 code

P0505 is a diagnostic trouble code (DTC) for "Idle Control System Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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P0505 code definition

Idle Control System Malfunction

What the P0505 code means

P0505 is an OBD-II generic code that the engine control module (ECM) determined the engine idle control system is not managing the idle to stay in specification. The idle is too high or goes too low.

What causes the P0505 code?

  • The idle air control (IAC) valve is carboned up and sticks or has limited control due to the carbon build up.

  • The IAC passages are clogged or restricted with dirt, debris or carbon build up.

  • The engine has a vacuum leak in the intake system after the throttle body that the ECM cannot control with the IAC.

What are the symptoms of the P0505 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.
  • The engine idle may be lower or higher than specifications.
  • The engine may idle rough if it has a vacuum leak.
  • The engine may stall when coming to a stop.
  • The engine may idle too high at times.

How does a mechanic diagnose the P0505 code?

  • Scans codes and documents the code in the ECM, clears and verifies the code

  • Monitors the engine idle to see if it stays within specifications in and out of gear and on road test

  • Checks the engine for vacuum leaks

  • Checks the engine for carbon build up on throttle plates and IAC valve inlet

  • Disconnects the IAC to see if the engine base idle is within specifications

  • Removes the IAC and check for blockage of passages

Common mistakes when diagnosing the P0505 code

  • Not verifying that the engine does not have a vacuum leak before replacing the IAC
  • Not removing excessive carbon in the IAC passages if replacing the IAC valve

How serious is the P0505 code?

  • Code P0505 is an indication the IAC is not working correct and it can cause the engine to idle too low or high and the engine may stall when coming to a stop.

  • The Check Engine Light being on causes the vehicle to fail emission testing.

  • The code may be from the engine has a vacuum leak and this can cause the engine to run rough and have poor fuel mileage.

What repairs can fix the P0505 code?

  • Replacing the IAC valve and cleaning the throttle body and passages
  • Removing carbon from throttle body and IAC passages and clean IAC
  • Repairing a vacuum leak in the engine intake manifold vacuum system or gaskets

Additional comments for consideration regarding the P0505 code

Code P0505 is for erratic idle and lack of idle control. The most common problem is a vacuum line to one of the intake or throttle body ports.

Need help with a P0505 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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