My '01 Ford Explorer idles at 2300 RPM in Park. When I switch to Drive, it goes down to 1600 RPM.

The Check Engine Light is on with code P1506.

I have replaced the MAF, IAC, sparkplugs, sparkplug wires, TPS, coil pack, and EGR valve. I have cleaned the throttle body,

Any ideas what might be causing this?

  • Are there any codes (check engine light)? Commented Oct 27, 2016 at 18:12
  • P1506 code and CEL is on
    – Martin
    Commented Oct 27, 2016 at 18:23
  • I already replaced the IAC Valve and checked for leaks. However I have not replaced the PCV, so I will try that next. Thanks
    – Martin
    Commented Oct 27, 2016 at 18:52
  • This trouble code can be caused by an air leak. Check the PCV valve; especially the rubber boot. Also, was the battery disconnected during maintenance? If not, the computer needs to be reset to recognize all the new components.
    – CharlieRB
    Commented Oct 27, 2016 at 19:36

2 Answers 2


The P1506 code is an idle air control overspeed error.

From autocodes.com:

The P1506 code means that the engine idle is out of factory specification. Sometimes the Idle Air Control (IAC) may have carbon built up. Disconnect the car battery, remove the valve, clean, re-install valve, and drive the vehicle for about 5 minutes with the headlights and A/C ON to get the idle relearned.

Also, check for intake leaks or stuck PCV Valve. If the problem persists, the IAC valve may need to be replaced.

So very simply, go through these steps:

  1. Diconnect the car battery.
  2. Remove the IAC Valve and clean it
  3. Put the valve back in
  4. Drive the vehicle for 5 minute with headlights and Air Conditioning ON.
  5. If that didn't work, check for intake leaks and PCV valve issues. I see you are about to do that. :)

Best wishes!

  • I guess I should have put another step in there: plug the battery back in! :)
    – anonymous2
    Commented Oct 27, 2016 at 19:01

This condition can be caused by a vacuum leak. Use an automotive safe spray such as carb cleaner to try to find the leak, both visually, and by noting changes in the idle speed depending where you spray it.

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