ABS sensor is at your brake caliper. it normally screwed on your knuckle arm to detect your wheel rotation speed. the 1 in your engine bay is ABS modulator @ pump.
This is kind of air booster, it keep extra air in the black thing....so when u revv,instead of sucking hard for fresh air.it wil easily get air from there. aftermarket air booster is way too expensive, so DIY is...