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P0505 Code: Causes, Symptoms, Diagnosis and How to Fix It

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P0505 Code is a very common OBD2 error code. To learn what it means, how to fix it, and what other codes it may show, keep reading. 

What is the P0505 code? 

The code P0505, which stands for “Idle Control System Malfunction,” means that the computer inside the engine can’t control the idle speed. As a result, the actual idle speed is not the same as the target idle speed. Most cars have a normal idle speed of between 650 and 750 rpm.

Idle air control valves (IACs) are commonly found on or near the throttle body of older automobiles. It is the IAC’s job to maintain the idle speed by measuring the amount of air passing through the throttle plate’s throat. The throttle plate closes when the car is idling, reducing the amount of air that may reach the engine. The engine, on the other hand, needs air to function. 


The idle control system opens the bypass air channel on the PCM’s orders. The throttle plate can be closed, but air can still flow around it and into the engine. The idle control system can regulate the amount of air given to the idling engine by varying the opening size of the bypass air channel. Idle speeds can be increased or decreased by increasing or lowering the flow of air. 

The PCM monitors the idling engine’s current load. When the engine’s idle control system is tinkered with, it gives it what it needs. Like other automotive parts, the idle air control system is subject to wear and strain. P0505 codes might be generated if the engine’s idle speed is adversely affected by this component malfunctioning. 

P0505 error code: Causes 

  • Carbon has built upon the idle air control (IAC) valve, which makes it stick or make it hard to control. 
  • The IAC passages are blocked or narrowed by a buildup of dirt, debris, or carbon. 
  • After the throttle body, there is a vacuum leak in the engine’s intake system that the ECM can’t fix with the IAC. 

P0505 error code: Symptoms 

  • The Check Engine Light will come on, and the code will be stored in the ECM memory. 
  • The idle speed of the engine may be lower or higher than what is called for. 
  • If the engine has a vacuum leak, it may have a rough idle. 
  • When coming to a stop, the engine might die. 
  • The engine may sometimes idle too high. 

Why is it important to control the engine RPM when it’s not moving? 

If an engine doesn’t have an Idle Air Control valve, it could stop. If the IAC valve is working right, it should increase or decrease engine RPM as needed so that the engine can make enough power to run all the electrical and mechanical systems in the car that depend on engine power. Some examples are the air conditioner, the audio/video system, the power steering system, the secondary air injection system (EGR), and various accessories.

If a car’s engine doesn’t have enough power to run these systems, it will probably work less well than it should and put out more harmful emissions than usual. It is mostly an engine that has to work hard to keep up with the rest of the car. The engine will start to stutter, won’t run smoothly, and will probably make the cabin shake. 

Before you even notice that the engine is about to start stuttering, the IAC kicks in and gives it a little more air, which makes the RPM go up and lets it keep up with demand. The engine’s RPM will go up just enough to keep it from dying, and it will stay at the right RPM as required by the engine’s maker. 

The RPM of the engine goes up when the IAC lets more air into the engine. The Power Control Module runs the IAC (PCM). The PCM tells the IAC valve what to do to keep the idle speed right as the engine’s needs change. The IAC has a metal rod and a plunger that move to either open or close the valve. The part is in a hole in the engine’s throttle body where air flows. 

P0505 Code

P0505 code: Diagnosis

  • Clears and verifies the code after it has been scanned and documented in the ECM. 
  • During a driving test, keep a close eye on the engine’s idle to make sure it stays within specs.  
  • Perform a vacuum leak check on the engine.  
  • Tread plates and IAC valve inlets need an inspection for carbon buildup. 
  • To see if the engine’s base idle is within specs, disconnect the IAC. 
  • Examine passageways by removing and inspecting the IAC.  
  • When diagnosing the P0505 code, there are a few common pitfalls. 
  • Without ensuring that there is no suction leak in the engine before replacing the IAC. 
  • IAC passages should be cleaned of excessive carbon if the IAC valve is replaced.

Is the P0505 error code critical? 

The IAC may be malfunctioning, causing the engine to idle too low or high or to stall when the vehicle stops. Vehicles that have the Check Engine Light on will fail emissions testing. In addition, having a vacuum leak in the engine might cause it to run rough and decrease fuel efficiency. 

Can I drive my car with a CEL light on and a P0505 trouble code? 

Error code P0505 needs a fix right away. Not recommended, but you can drive your car even if the trouble code P0505 is on unless the engine stalls or stutters in a way that makes the car hard to drive. There may be errors or a lack of control over the idle speed. A vacuum line to one of the intake or throttle body ports is the most prevalent problem. Before replacing the IAC, you don’t check to see if the engine has a vacuum leak. If you are replacing the IAC valve, you should not leave too much carbon in the IAC passages. 

What can be done to fix the P0505 error code? 

  • Replaced and cleaned throttle body passages with a new IAC valve.
  • Inspecting and perhaps repairing a vacuum leak in the intake manifold or gaskets.

Is it safe to drive with a P0505 code engine? 

Driving with a P0505 code engine is generally safe, but it can cause some issues, depending on the severity of the problem. If the idle speed is too high, it can be difficult to slow down or stop the vehicle. If the idle speed is too low, the engine may stall when stopping or idling. 

How often does a P0505 code engine occur in my vehicle? 

It is difficult to say how often this code might occur in your vehicle, as it can depend on several factors, such as the age and condition of your vehicle, how often you drive it, and how well it has been maintained.  

Can you prevent a P0505 code engine?

Yes, here are some methods to resolve this engine problem 

  • Regular maintenance 
  • Keep your air filter clean 
  • Check your intake system 
  • Drive safely 
  • Address any engine problems promptly 

Can a P0505 code engine cause other problems in my vehicle? 

Yes, with a DTC P0505, your car may stall randomly at stop lights or in traffic. You may also notice a decrease in your fuel economy over time. Furthermore, driving with this issue code will cause additional damage to your car’s engine. 

What happens if you remove the idle air control valve? 

Removing the IAC valve from your vehicle can lead to various issues, including engine stalling, difficulty starting, poor fuel economy, and a check engine light. We don’t recommend removing the IAC valve unless you have a specific reason to do so and know how to compensate for its absence. 

How much does it cost to replace the idle air control valve? 

On average, the cost of the part ranges from $50 to $300, with labor varying from $50 to $200 per hour. So, the total cost can range from around $100 to $500 or more. 

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