Did your mechanic move the air cleaner, because the box is under there, did you saw the picture, I think what your mechanic is done, he actually turn the idle air mixture, not so much effect, like the black box actually does, is riches all rpm's and you should feel the difference if everything goes right, dont drop little O- rings. I opened my exhaust little, feel more difference and car performing so nicely now, more smooth and stable idle too.