Okay...I kinna know what it does but I need to know if it needs to be there for the car to function normally.

It's mounted on the N/A S5 UIM...it has a coolent in and out...It pulls air from the upper intake hose...it's held by two 10/12mm bolts.

Been trying to find a pic but no luck.

 

You talking about the BAC valve?

 

Yep, that's the Bypass Air Control valve. Basically it's what the ECU uses to control the idle speed. It allows more air to bypass the closed throttle plates when you use the A/C, headlights, heater fan, rear demister, etc.

 

Thats what I was thinking... if you dont have ac, power steering, or the stock fan, your car will be fine without it. It adjusts the idle depending on the load put on your car at idle. If you removed it and you still have those 3 things, then your idle could get kinda funky.

 

damn...I only got one and then two cars to build...shitmonkey! I guess I'll just have to buy another later.

Will one from an S4 work with an S5 car?

 

You don't need to take off the stock fan to remove the BAC I still have it and my idle is fine all it has to do is warm up and it is fine. I had removed the BAC when I still had Power steering and it was fine with that also: never stalled on me or studdered.

 

When you used your A/C did the idle change, or did you not have A/C?