hey all, just went out to start the ol bronco up and noticed the idle was dropping down below 800 rpms, and when it did, I heard a loud sucking noise coming from one of the breather holes right in there by the plenum in the throttle body.
forgive me for not knowing what those holes are called. one goes up to the passenger side of the intake manifold and the other goes down to the top of the driver side valve cover.

the one going to the intake is the one making this hideous noise. it makes the sound when the engine is at low rpm and struggling to stay alive. it also makes this noise anytime the car is in gear.

it is a 1986 ford bronco ii xlt. 2.9L fuel injected V6

any insight would be appreciated!
-Morgan

 

update: cleaned throttle body and idle air bypass valve and hoses. still making the noise

 

The noise is probably vacuum leaking. Check for cracked or ill fitting hoses.

 

hey Pete, if you cover the hole that goes towards the IAC, you can feel the suction. could a vacuum leak cause the iac to try to suck more air? because all of my vacuum lines look fine.

 

the problem was a crack in my air filter housing, down where the fresh air intake connects to the bottom of the filter.

thanks