Hello,

I have received the error code P1506 on my 1999 F150 which is I believe an idle air control overspeed error. It seems to run a little rough at idle but not too bad. At the advice of my Haynes repair manual and the advice of a friend I have already replaced the IAC valve and the PCV valve on the engine and cleared the code, only for it to come back again after 50K miles.

I am not sure where to go next with the diagnosis/fix. Any help would be much appreciated.

Thanks!

 

Good chance you have a vacuum leak although that usually results in other symptoms.