Mystery sounds and stalling issue

[Bayalyka]

Hey guys! First time expy owner, and I'm having some issues I can't figure out. There's a stalling issue that occurs at idle when the engine is cold, if I brake hard, or if I'm in reverse. I cleaned out the iac valve and replaced the gasket but the issue hasn't gone away. I also have this loud buzzing noise when the car is in gear, I'm thinking maybe something with the trans? At first I thought ac compressor but the sound is still there even when the air con is off. Thanks for your suggestions!
**UPDATE** buzzing noise occurs only when in park or drive, not neutral

 

[Petesexpy]

Check intake manifold gasket. When a mechanic changed mine, he said it literally fell to pieces.

 

[Vincent Vega]

The first things I would check are the throttle body and the MAF sensor. These are the simplest issues that can cause idling problems like you are having, if they get dirty. Hard to say what the buzzing is without hearing it, although what @Petesexpy said is worth a look because the intake manifolds and gaskets do go bad on these (mine did). The EGR would be thing place to check, and vacuum leaks in general. Good luck.

 

[FlyBry]

Easy to check the manifold gasket for leaks by spraying it with starter fluid while engine is idling.