"DTH ( k + 1 ) = a1 ??? DTH ( k ) + a2 ??? DTH ( k - 1 ) + b1 ??? DUT ( k - d ) + c1 ( 1 ) where k is a parameter representing a discrete sampling time or a discrete control time which is digitized with a first period ??T1, and DTH(k) is a throttle valve opening deviation amount defined by the equation (2) shown below." . . . .