Mitsubishi Lancer P0505 - Idle Air Control System - Malfunction

P0505 This OBDII code deals with the idle control system of the Mitsubishi Lancer.  It’s a generic code, which means that it has the same meaning for the Lancer as it would any other vehicle (Lancer or not).

P0505:  Idle Air Control System:  Malfunction

P0505 usually occurs due to a stuck idle valve, a blocked idle valve control valve, or an unattended vacuum leak.  However, there are other possible causes.  Although, they aren’t as prevalent.

P0505 Mitsubishi Lancer


Índice de Contenido
  1. P0505 Symptoms:  Mitsubishi Lancer
  2. Lancer P0505 Causes
    1. Valve to control the idle airflow
    2. Vacuum Leak
    3. Carbon Buildup
  3. Conclusion

P0505 Symptoms:  Mitsubishi Lancer

This particular trouble code lets you know that there is something wrong with the idle air control system, but that’s about it.  The symptoms may vary.

These are the top symptoms of P0505.

  • Soon, Service engine light
  • Don't be rough
  • Stalling
  • Very high idle speed 


Lancer P0505 Causes

P0505 can usually be traced to either a vacuum leak or an issue with the idle control valve.  While replacing the idle air control valve seems like a good idea, it’s worth your time to check for a Leakage of vacuum first.

Mitsubishi Lancer P0505 Diagnosis

Valve to control the idle airflow

The idle air control valve’s primary job is to regulate the idle speed of your engine.  The idle air control valve regulates the engine's idle speed by controlling the amount of air that is allowed in.

You can either get the IAC valve stuck or dirty.  It may be necessary to replace it or clean it.  Here’s a great You Tube video How to clean an idle air control valve  

You may need to replace your idle air valve if you feel it is time. It is very affordable.


Vacuum Leak

While the idle air control valve is often the cause of P0505, it’s a great idea to start diagnosing it by looking for a vacuum leak.  Check the vacuum tubes surrounding the IAC.  It may be necessary to replace them if they appear cracked or dry-rotted.

Leakages around the throttle body and intake manifold can cause your Lancer's code to be thrown.  Here’s a great article from Popular Mechanics on How to spot a vacuum leak.


Carbon Buildup

It is possible for carbon to buildup in the IAC intake area.  It is possible to fix this problem by checking the IAC inlet area for blocked passages.

The throttle body can become too dirty to allow air to enter the engine.  This can cause P0505 to be thrown.  Often, when this is the case, you’ll feel the engine stall for a second before it recovers when slowing down.  

This happens because the engine can’t adjust to this problem fast enough.  This problem is usually solved by cleaning the area around the throttle blades.



You will be able to diagnose P0505 on your Lancer.  Most of the time it’s a vacuum leak or the idle air control valve.  If you feel like there’s anything that you can add, please feel free to leave a comment below.

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