My 2001 F-150 w/4.6 was coding a bad EGR. Took it off and cleaned it. Engine light gone. But now I have a strange hummimg sound that occurs only when RPM are dropping. As in coming up to a stop. Usually only lasts a few seconds. But occasionally as long as 30 seconds. Any ideas?

 

Hard saying....but taking a stab at it.... it might be that the IAC needs cleaning as well, can't hurt. Best way to clean the IAC is to remove the throttle body housing ( the IAC will come with it, note the condition of the PCV elbow as well), and clean the whole housing and then remove the IAC ac clean it. There is 2 EGR ports inside that can get pretty clogged up too.

..or you got a leak from cleaning the EGR??