Error Code P1506 is defined as Idle Air Control Overspeed Error. This code means that the engine idle is out of factory specification
This error code is a manufacturer-specific trouble code, meaning it does not apply to all cars makes. Rather, it applies only to specific 2012 Mitsubishi Eclipse spyder makes, such as Ford. Specification on the definition, troubleshooting, and repairs still vary from one make and model to another.
The IACV or Idle Air Control Valve assembly works by controlling the engine’s idle speed and provide a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM (powertrain control module, also known as ECM or engine control module) determines the desired idle speed or bypass air and signals the IAC valve assembly through a particular duty cycle. The IAC valve then responds by positioning itself to control the amount of bypassed air. The PCM monitors engine RPM and increases or decreases the IAC duty cycle for it to achieve the desired RPM.
Error Code P1506 is set when the PCM detects an engine idle speed that is out of the specifications (higher RPM) set by the manufacturer. Sometimes, the IAC can have a carbon build up.
As with other error codes, this error code activates the Check Engine light and registers the code to the system.
Possible causes for this code include:
The first thing you need to do is help your 2012 Mitsubishi Eclipse spyder re-learn the idle. You can do this by disconnecting the battery, removing the valve, cleaning and re-installing the valve and then driving your 2012 Mitsubishi Eclipse spyder for around 5 minutes with both headlights and A/C on for your 2012 Mitsubishi Eclipse spyder to relearn the idle.
Also, check for leaks in the intake or check whether the PCV valve is stuck.
It is important not to start with an idle air control valve (IAC) replacement when you have this code, because in many cases the problem is caused by lots of vacuum leaks, and can cause serious idle problems. Air leaks into the engine after the MAF has already metered the incoming air, causing the O2 (oxygen) sensor to see very lean exhaust. Since your 2012 Mitsubishi Eclipse spyder is at idle, the computer will try to reduce incoming air by shutting the IAC down. When it commands for less air, and your 2012 Mitsubishi Eclipse spyder still idles high, it will set the error code.
In this case, the usual cause of the problem is air leaks in the rubber hose.
Start your diagnosis by replacing both the PCV and the hose. Many people report that their 2012 Mitsubishi Eclipse spyder doesn’t stop this hose.
If the problem persists, then you need to replace the IAC valve.