I am currently hearing a rather loud sound coming from my engine, which sounds like a kettle boiling or a dog whistle. I don't know what is making the noise, but this coupled with my recent drop in fuel economy and power makes me think something is up. Also, about a week ago I heard a strange depressurizing sound in my engine bay that I had never heard before. I popped the hood a couple of minutes ago after hearing it whine all the way home, and I have a picture of where it is coming from. I have next to no knowledge of engine mechanics, so any assistance would be helpful.

Could be the idle air control valve

Does that valve shut when the accelerator is depressed? I tried blipping the throttle and it changes pitch and sort of goes away at even a tiny bit of rpm

My IAC whistles a bit when cold on my new throttle body. Also check the EGR vacuum under the drivers side TB if its off it can whistle a little bit.

Check out the bearing on the back of the alternator.

One way to check to see if it is a bearing on the alternator is to get a mechanics stethoscope. But I think it may be a vacuum line. If it is a vacuum line downstream of the throttle plates then as you depress the throttle, manifold vacuum will decrease, causing your noise to disappear. Take your foot off the pedal, manifold vacuum increases and you hear the noise again. I had a problem similar to yours on my 76 Camaro many years ago. Discovered a cracked vacuum line.

Thanks for the help so far! I just turned the car on again to check and the sound is gone. I'll post again tomorrow, seems like it only wants to whistle when it's hot.

Check for harmonicas.

Haha, nice one. Bet you've been storing that one in you back pocket for such a time as this

could be PCV valve if it is shot, they rattle inside a bit. my thought though is that if it changes with the throttle, i'm on team alternator.

BTW the facebook post screenshot there is epic!

Ha! I saw it posted on FB at the same time I saw this thread.

I did my best to take a better listen to the engine today, and I stuck my ear right up to the throttle body while the engine was running and that's where it was loudest, I heard nothing from the alternator. It seemed to be coming from right around the area where the throttle cables are attached. I don't know what would make a whistle here though. Maybe a bad seal?

Oour TBs are known for throttle shaft wear.

I would suggest looking up the minimum idle set or IAC reset procedure. Force you IAC closed and run the engine. See if it changes pitch.

Also, does you idel seem higher now?

Get some starter fluid, start spraying suspicious areas and see if the RPMs picks up. * Don't soak the engine down, the ether is very flammable! Use it lightly in the area you want to test.

I literally LOL'ed

Reminds me when we put a heavy duty zip tie on the driveshaft of some jerk's Jeep Cherokee we worked with.

Thwap thwap thwap,

The idle is the same as it was always been. How does one go about forcing the IAC shut? It's located on the passnger side of the throttle body correct?

Minimum Idle Set or IAC Reset

It is here

Or Here

Are you data logging? Can you compare previous IAC counts to where they are now? Your leak may not be big enough to upset the idle (Yet) but the IAC isn't opening as much as it used to. Just a thought.

I had a pcv valve that whistled real loud, pull it out and put your finger over it and see if the noise disappears.

Don't discount a vacuum leak. Get a length of hose and put one end in your ear, poke with the other end around the throttle body to help pin point the location.

The 5.0L in my '88 Econoline had developed an annoying whistle. No outward signs of anything wrong - no rough idle, etc. Didn't really notice a drop in fuel economy but being a truck it really isn't something that's on the radar.

Tracked it down to a vacuum leak in the plenum to manifold gasket.

I'm laughing so hard that I'm crying. Thwap, thwap, thwap - I LOVE IT. Now who can I do this to?

Best part is, it wears out and goes away.

Turns out it was the gasket behind the throttle body that was leaking. Anyone know where I could find one? I've looked online but I don't know the right size. Thanks for the help, and it's nice to see some humour in your posts lol

Felpro 60655 for 85-88 tpi