I have a 2005 FX4 with a 5.4 Triton, it has a little over 200,000 on it. Last week it started getting a little doggy when idiling and i was backing out of driveway and it almost died and the check engine light came on. called local town mechanic and he said that he wouldnt work on this year and motor. i went to oreillys and they read the code and it was P0506, idle air control valve. the only thing is the 5.4 doesnt have a idle control? is there anything i can clean or look at? help much appreciated!

 

That code means the PCM can't control the idle speed. Most likely the throttle body has carbon deposits restricting the airflow at idle. Take the TB off and clean it real good with some carb cleaner and a old toothbrush.

 

I'm having exact same problem, coughing and sputtering at idle. Would you mind posting any results you have. I changed my plugs yesterday.. $1100 later, I still have idle trouble.