Several weeks ago I put a K & N ENGINEERING, INC. Air Filter on my 2004 4.6 F-150. Several days ago the check engine light came on and I found the problem code was PO506 Idle Control System RPM Lower Than Expected.
Does this new fliter have anything to do with this? The truck has 137,000 miles on it. If the filter is not the problem what is the solution?

 

do you have a tuner in it?
try cleaning the throttle plate. that tends to help alot on the electronic throttle bodies.