hey guys, a buddy of mine has a 2WD 97 F150 short cab stepside with the 4.6L, and it's stick. he and i just put on an intake kit, first mod the truck's seen. it's a cone filter with a circular stainless tube going from the filter to the throttle body, and it has ports for the vent lines and 2 sensors (MAF or something, don't know which one does what). the truck runs with it installed but on decel when the engine gets close to idle there's a horrible humming noise coming from inside the intake tube, it can be heard in the cab too. sounds like a resonation or vortex issue, but we're not sure. it also holds RPMs up higher than idle without any throttle input. any ideas as to what's making this sound? we took the filter off while it was doing it and it's still humming. if the throttle is blipped hard, it stops when the engine settles back down. really strange. any thoughts?

 

i have run into the same problem with a K&n intake. The noise comes from the IAC motor or idle air control motor. i cleaned mine with carb cleaner and the noise went away. the noise came back later though. the only reason i can think of is because the k&n eliminates the filter for iac and the dirt gets in it over and over.

 

there was a little black plastic box that was in one of the two hoses going from the stock intake tube to somewhere on the engine (i forget where). we removed that little box, and i have no idea what it was for. would that have anything to do with it?

 

yes i believe that little black box is a filter for the idle air control motor. the part that is making the humming noise.

 

leftover parts usually means issues

 

how do you clean the idle air control motor?

 

http://www.fordf150.net/howto/throttlebodyclean.php

Read throughout. It's towards the end.

 

If i remember right on my k&n it said if the black box made noise to take it off. So it must not be that important.

 

thanks a lot for that link. there are 2 hoses that go to the intake tube. i guess one is for the IAC motor, based on what you guys have said. what's the other for?

 

reinstalled the little black filter box, fixed everything.