a manual selector of the automatic transmission is placed the output signals of the throttle opening degree sensor 12 engine revolution speed sensor 14 idle switch 15 and selector position indicating switch 18 are fed to a microcomputer based control unit 20 in the control unit 20 execution of a routine shown in fig2 is effected based on at least some of the output signals fed to the control unit 20 to correct the output signal of the throttle opening degree sensor 12 this routine is initiated by a command for effecting the correction in fig2 at a step 52 times tm1 and tm2 are started subsequently at a step 54 reading operations of the output signals of the sensors 12 14 and switch 18 are performed there is then an interrogation 55 as to whether or not a rate of change dth i e th a stored throttle opening degree data is less than a predetermined value dth 0 if dth is not less than dth 0 the routine proceeds to an end point if dth is less than dth 0 there is an interrogation whether the content of the time tm1 has reached a predetermined time value t1 or not if this is the.