Toyota 4Runner P0505: Idle Air Control System- Malfunction

P0505 is an OBDII code that deals with the idle air control system in the Toyota 4Runner.  It’s a generic code, which means that it has the same meaning for the 4Runner as it would any other vehicle (4Runner or not).

P0505:  Idle Air Control System:  Malfunction

When P0505 is triggered, it is typically caused by a stuck idle air control valve, a clogged idle air control valve, or a vacuum leak.  There can be other causes as well.  Although, they aren’t as prevalent.

P0505 Toyota 4Runner


P0505 Symptoms:  Toyota 4Runner

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

Here are some of the most common symptoms of P0505:

  • Service engine soon light
  • Rough idle
  • Stalling
  • High idle speed 


4Runner P0505 Causes

Typically, P0505 is going to be caused by either a vacuum leak, or a problem with the idle air control valve.  While replacing the idle air control valve seems like a good idea, it’s worth your time to check for a vacuum leak first.

Toyota 4Runner P0505 Diagnosis

Idle Air Control Valve

The idle air control valve’s primary job is to regulate the idle speed of your engine.  It does this by letting in just the right amount of air to get the idle speed where it needs to be.

The IAC valve can get either dirty or stuck.  You may need a new one, or you may be able to get away with cleaning it.  Here’s a great YouTube video on how to clean a idle air control valve.  

If you determine that you need a new idle air control valve, they are relatively 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.  Inspect the vacuum tubes around the IAC.  If they look cracked or dry rotted it may be time to replace.

Intake manifold leaks, and leaks around the throttle body can also code your 4Runner to throw this code.  Here’s a great article from Popular Mechanics on how to find a vacuum leak.


Carbon Buildup

The IAC inlet area can get carbon buildup on it.  Inspecting the area around the IAC for passages blocked with carbon can often fix the problem.

If the throttle body gets dirty enough, it can change the amount of air able to get into the engine.  It can throw P0505.  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.  Cleaning it around the throttle blades will solve the problem in this case (most of the time).



Good luck diagnosing P0505 in your 4Runner.  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.