An operation control system for an internal combustion engine having an intake system, a throttle valve including a first rotary shaft rotatably arranged in said intake system and a throttle valve body provided on said first rotary shaft for rotation in unison therewith, and an accelerator pedal for adjusting the valve opening of said throttle valve, said operation control system comprising in combination:
- mechanically connecting means operatively connecting between said accelerator pedal and said throttle valve,
- said mechanically connecting means having a second rotary shaft disposed for rotation through an angle directly proportional to a change in the stepping amount of said accelerator pedal,
- said mechanically connecting means being operable such that an amount of change in the valve opening of said throttle valve relative to a change in the stepping amount of said accelerator pedal is smaller when said accelerator pedal is in a smaller stepping amount region than when said accelerator pedal is in a larger stepping amount region;
- a throttle valve opening sensor adapted to generate as actual throttle valve opening an output signal directly proportional in value to a stepping amount of said accelerator pedal,
- said throttle valve opening sensor being mounted on said second rotary shaft such that said output signal therefrom represents a circumferential position of said second rotary shaft;
- and
- control means responsive to said output signal from said throttle valve opening sensor for controlling an operating amount of said operation control system.