Subaru Forester P0506: Idle Air Control – RPM Lower than Expected

P0506 It is the most common OBDII code. This is most commonly triggered when engine idle speed falls below the manufacturer-predetermined limit.

It's a generic cod, meaning it can be used to refer to any code. Subaru Forester As it would for any other vehicle.

 P0506 Symptoms:  Forester

P0506 is usually not noticeable while driving. These are some of the symptoms that the Forester may present:

• Coming Soon: Service Engine Light– The reason why you are here.
• Lower idle speed– Assuming that the code has been thrown due to a legitimate issue, you should notice the engine running slower when not pushing the gas.
• Stalling–  The idle may be too slow for the car to run without pressing on the accelerator pedal.

Subaru Forester P0506 Diagnoses and Causes

Many possible causes of P0506 exist. While the code specifically mentions the “Idle Air Control System”, it would be a mistake to just go ahead and replace the idle air control valve without a little due diligence. It’s not always the cause of the code.

Below are some common problems that can be caused by P0506 on the Subaru Forester. We also have the information you need to help fix them. There are many model year differences. You might start with looking at a Vacuum leak From there, you can move on.

Vacuum Leak

Leaking vacuum systems can cause Foresters to idle more. The vacuum system can leak, causing the combustion chamber to lose its air balance. 

How to find a vehicle vaccum leak (Popular Mechanics, Article)
Find a Vacuum leak in under a minute (2CarPros, YouTube)

Bad things can cause a vacuum leak vacuum hoseIt is the Intake is endless, EGR SystemOr anywhere air can flow through. It’s not hard to find a vacuum leak though. Use the resources above and you’ll find it in no time.

Valve to control the idle airflow

The majority of modern fuel-injected engine are fitted with an idle control valve. Some engines are not equipped with an idle air control valve. If you have determined that you don’t have a vacuum leak, the IAC is a great second place to troubleshoot P0506.  You can find idle air control valves here It is very affordable.

How to diagnose an IAC valve (Autozone Guides)

Throttle body

The throttle body can be opened and closed millions of times during the lifetime of a car's engine. It can collect dust from all the air passing through it. The vehicle's idle performance can be affected by this grime. When dirty, you’ll often feel the vehicle almost stall before the computer compensates and opens it a little more.

If the throttle body is damaged or not functioning properly, then the code can be thrown.

Here are some signs your Throttle Body is failing and what to do (Repair Pal)
What to do if your throttle body is dirty or bad? (YouTube Auto Repair Youtube)

Blockage of Intake or Exhaust

The idle could drop to P0506 due to a problem with the catalytic convert or the intake manifold. 

Conclusion

The P0506 problem is serious. It is dangerous to drive with an engine that could stall in any weather condition. We strongly recommend you have your Forester serviced ASAP. We wish you all the best!