Error Code P0511 is defined as Idle Air Control Circuit. Meaning, the engine’s RPM is having an abnormal condition when idling, due to defective valves, faulty electrical wiring, or a severe leak.

This is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system or made since 1996 up to present. It is common among, but not limited to, Dodge, Chrysler, Hyundai, Jeep, Mazda, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

This code means the PCM has detected a problem with the IAC (intake idle air control) circuit. If there are other more specific codes present along with this code, then those codes must be addressed first.

Revolving around a linear servomotor which controls a plunger, the IAC system works by regulating the amount of air allowed to bypass the throttle plate and enters the intake manifold. This way, the engine RPM at idle is also controlled. When the throttle plate is closed (at idle), the throttle body only allows a very small amount of air to pass through. The engine will not be able to continue it’s idle and will eventually stall. Thus, there’s an auxiliary air (vacuum) source provided for the engine to continue its idle while the throttle plate is closed. Obviously, this auxiliary vacuum source is detrimental to both the engine performance and fuel efficiency when the throttle plate is opened (upon acceleration). Hence, there a fully adjustable vacuum source is controlled by the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes).

The housing of the IAC valve plunger is made with two separate openings that allow air to pass through them. This valve is usually bolted to the intake manifold, on or near the throttle body. It is positioned in a way that when it is open (the plunger moves out of the opening), the ambient air flows through and into the manifold when it is closed (the plunger fills the opening) ambient air cannot flow through it.

The IAC is seldom completely open or closed, but it’s in constant motion, which is controlled by the PCM. The PCM uses input signals from the O2 (oxygen) sensors, TPS (throttle position sensor), and other sensors to determine how much air should be allowed to bypass the throttle plate. As the PCM adjusts the voltage and ground signal to the IAC valve, the valve reacts accordingly. If the engine RPM levels don’t coincide with the specifications and limitations set by the manufacturer, then the Error Code P0511 will be set, and activate the Check Engine light.

Other related Idle Air Control System Circuit error codes include:

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:

  • Engine stalls, especially at idle
  • High engine RPM level
  • Unusual noises coming from the throttle body area

In some cases, other IAC related codes may be present.

Possible Causes

Possible causes for this code include:

  • Open or short in the IAC connectors or control wirings
  • Defective IAC motor/valve
  • Engine vacuum leak
  • Carbon buildup in the throttle body or IAC valve
  • Defective or programming error in the PCM

How to Check

To diagnose this code, you will need to connect the scanner to record data of the vehicle and identify concurrent faults.

Then, clear the codes and then take the vehicle for a road test to see if it comes back and identify an intermittent condition.

Next, conduct a visual inspection of the IAC connectors, wirings, and look for any signs of loose connections or damages.

Open the IAC motor manually using the scanner. Then, test the IAC motor connector voltage.

Check the throttle body for coking and carbon buildup. Coke is a greasy black substance that causes a blockage.

How to Fix

Depending on your diagnosis, common repairs for this code include:

  • Repairing of damaged wiring or connections
  • Repairing the IAC valve
  • Cleaning the throttle body bore or replacing the throttle body
  • Diagnosing and repairing any concurrent DTCs

One of the most common mistakes in dealing with this problem is replacing the idle air control parts without making sure that the throttle body is not restricted. Sometimes, a simple cleaning can fix the problem. However, required chemicals can also cause damage to the surrounding connectors and wirings, which is why replacement is the most viable option.