this can make ur engine vibrate on idle if u adjust it wrongly..it just simulate the carburetor adjustment on fuel injection car..kind of funny huh?..btw,this thing just make ur car drawn in more air by using PCV hose..if u put it on very intelligent car(BMW,MERC,VOVLO) it will detect air leak on engine side and bring the engine warning lights on problem because the air entered in ur engine is calculated by engine air mass sensor already..