Nothing to do with air injection............
It's to raise the idle speed (or to keep the idle from being too low) when the engine is cold by letting extra air bypass the throttle plate.
You can compensate by having a slightly raised idle speed at normal temp, so that when the engine is cold it's not too LOW.
I'd rather remove it if it's non functional, but will leave it in place (although non-functional) if it's considered smog equipment.
