what does ait do and do i need it if i am gonna do teh throttle body mod, wehre u remove the double throttle plates, and also how do i disable the cold start?

 

Keep your engine running to disable cold starting.

 

The BAC adds air to the intake at idle while the A/C is one to bump the RPMS up, and keep the car idleing smoothly.

If you don't have A/C, you don't need the BAC.

 

BAC: turning with wheels with power steering, or having the A/C on, puts load on the engine. Load on the engine at ilde means a drop it idle speed. To keep the speed up the bac takes metered air and puts it into the intake manifold, since the throttle plates cannot change their position. If you have removed a/c and p/s, you don't really need the BAC.

BAC and TB mod are hardly related.

Cold start: on s5 cars, start your car in first gear.
on s4 cars, I think you unplug the sensor at the bottom of the rad, but you'd have to verify with one of the s4 guys, as I don't pay as much attention to them.

 

is BAC emmisions related at all?

 

Do you turn your wheels or have your a/c on during idle testing for emissions? if not, nope.