P0506 MERCURY Idle Speed Control System RPM Lower Than Expected

Possible causes
– Dirty throttle body
– Electric throttle control actuator misadjusted or damaged
– Faulty Electric throttle control actuator
– Intake air leak
– Poor electrical connection to the Intake Air Control (IAC) valve
Tech notes
If there are no intake leaks, clean throttle body, adjust engine idle and erase engine code. If the code comes back you may have to replaced the Electric Throttle Control Actuator (Motor) to repair the problem.

There is a factory service bulletin for the following Mercury Models:

2005-2007 Grand Marquis
2006-2007 Mountaineer
Mercury Factory Service Bulletin OBDII Code P0506

When is the code detected?
The idle speed is less than the target idle speed by 100 rpm or more.
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
– Engine hard to start
– Rough or erratic idle speed
P0506 MERCURY Description
The Engine Control Module (ECM) controls the engine idle speed to a specified level through the fine adjustment of the air, which is let into the intake manifold, by operating the electric throttle control actuator. The operating of the throttle valve is varied to allow for optimum control of the engine idling speed. The ECM calculates the actual engine speed from signals of crankshaft position sensor (POS) and camshaft position sensor.
The ECM controls the electric throttle control actuator so that the engine speed coincides with the target value memorized in the ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warming up, deceleration, and engine load (air conditioner, power steering and cooling fan operation, etc.)
MERCURY Technical Service Bulletins for P0506 code
2004 MERCURY MOUNTAINEER ENGINE (PWS)
2005 MERCURY GRAND MARQUIS ENGINE (PWS)
2005 MERCURY MOUNTAINEER ENGINE (PWS)
2006 MERCURY GRAND MARQUIS ENGINE (PWS)
2006 MERCURY MOUNTAINEER ENGINE (PWS)
2007 MERCURY GRAND MARQUIS ENGINE (PWS)
2007 MERCURY MOUNTAINEER ENGINE (PWS)
2008 MERCURY GRAND MARQUIS ENGINE (PWS)