Hey guys, I have a 2000 f-150 reg cab short bed xlt with the 4.6 and auto tranny and over the past few months its been making this LOUD humming/buzzing noise from the intake ever since it's gotten cold up here in western Pa. It sort of sounds like a tug boat horn or something along those lines. It always does it when the truck is in drive or reverse when you're either pulling out from a stop or leave it coast for a short period of time. When I pull out from a stop it makes the noise until i give it gas then goes away. It will also make the rpms surge to 1000 rpms if you let it make the noise too, but it goes away everytime you hit the gas. I have a K&N cold air intake on the truck and the noise is loud as can be coming from the filter. When inside the truck it sounds like its coming from the back of the motor on the passenger side. My mechanic told me it could be a vacuum leak on the back of the intake manifold possibly? I tried checking for a vacuum leak by spraying everything with brake cleaner and it never stalled so I guess thats not the problem? What do you guys think it could be? The IAC valve???

Also, my truck has a very poor brake pedal! it had no brake pedal pressure at all when I bought it wrecked. It was hit lightly in the drivers side cab corner when i got it, but anyways The ABS light has been on in it since i bought it. I've replaced the master cylinder with a junkyard one, and it got some brake pedal back. I then repaced the power brake booster thinking that was the problem and its still the same. When I bled the brakes after changing the booster my brake warning light came on (the red light with the brake!) and stays on most of the time, but once in a while it'll shut off then come back on but the ABS light is still on. If i pump the brakes up I get good pressure or if I slam them the pedal is hard, but if I just brake normally the pedal goes to the floor, but the truck stops fine? I know the abs doesnt work becuase it'll lock the wheels up if i slam the brakes. My mechaninc told me that my drivers side front caliper is the only one with the caliper slides that move. The other 3 do not move. He said that could possibly be the problem? My buddy, his dad, and uncle are mechanics for a living and we're all stumped with this trucks brakes...but they're Chevy guys :P. Any idea what you think could be causing this problem as well?

I appreciate any help you guys could give me I just put a pile of money into my truck and I love my truck, but I'm a fresh college graduate and cant keep blowing money trying to fix everything on it like ive been lately because I have bills to pay and am still looking for a better job than the 2 I have now but if you guys could lead me in the right direction or help me narrow it down I'd gratly appreciate the help! Thanks!

I have a vidoe of the noise my truck is making if you send me an email address I could send it to you!

 

Your IAC (idle air control valve) is what is making the noise. You can try cleaning it and see if that makes it go away. Does not affect driving until the truck is hard to start.

Your brake issue is a different matter. Yours is 4 wheel anti-lock which is different from mine. Have you read the code from the ABS light? I would start there.

 

Bleed the brakes again. Then do it again. Then one more time.

The IAC is just a little valve, doubt it's buzzing. My PCV valve buzzes like a freak, not sure if that's normal or not.