ok, first off i have a 1997 F-150 4.6 with 205,000 miles on it.. stock engine and tranny. its been a great truck and never given me any major problems. But recently something under the hood (wish i could be more specific) makes a really loud HUMMING noise (almost sound like a trumpet). for example- say im driving on the highway and i let off the gas, this humming noise will appear and it is very loud, but right when i give the engine some gas the humming goes away. or also when im driving through town, when i come to a stop light, let off the gas to apply the breaks, this humming noise will come about. what i have to do is stick the truck in neutral and give it a big rev (which i do like hearig my exhaust so it isnt always annoying) and then it stops. note though, it doesnt happen every single time i let off the gas, however it is pretty frequent.

do yall think this is in the air intake system? thatd be my only guess because when i rev the engine it quits, but one thing is it sounds like it comes more from the passenger side of the truck, and it seems to occur more often when the temperature outside is cold. im completely stumped by this one, ive never heard anything like it. any ideas or info would be GREAT.

Thanks!!

 

SOUNDS LIKE THE PCV VALVE OR IDLE AIR CONTROL VALVE IS RESONATING

 

yea, i think its vacuum related, thats why it changes with throttle position.

 

is this somethin i should be able to possibly fix myself??

 

ill ask you too, i know the pcv valve is an easy fix, what about the valve you mentioned?

 

hey my truck did the same thing. it's the pvc valve. real easy replace.

 

if i aint mistaken, the pcv valve is on the right side of the engine??? which is where it seems to be coming from

 

THATS IT.STICKS OUT OF THE TOP OF THE VALVE COVER.YOU SHOULD BE ABLE TO SWAP IT OUT IN THE PARKING LOT OF YOUR FAVORITE PARTS STORE

 

you pretty much 100% sure??? thanks

 

Also could be a leak in the induction system, particuarlly in the air cleaner housing, inlet tube causeing resonance between the 'normal' air source and the leakage source,

 

a bad pcv valve would be one good guess since the vacuum in it changes with throttle position..

 

https://www.ford-trucks.com/forums/9...s-removed.html

 

Wonder if the problem was ever found and solved. I've read about this since I'm having he same issue....replaced my pcv valve and that seemed to fix it only for a bit. Its still there just not as often. All the hoses/tubing seem in very good condition...any other ideas?

 

When its making that "mooseing" sound, unplug the IAC and see if it stops instantly.

 

I would start your own thread, this will keep this from getting confusing.
The original noise discribed and the way he stopped it was very telling to me. I'm surprised the fan clutch did not come up.
The PCV valve is common to make weird noises. As is the air intake for resonating in a moose type moaning noise.