| 摘要 |
PURPOSE:To reduce an output fluctuation due to a change in air-fuel ratio by changing an air-fuel ratio control means over to the lean side in step rather than to a theoretical air-fuel ratio, and opening and closing a valve device within a bypass passage bypassing a throttle valve with a control means. CONSTITUTION:When an engine 1 is running, ECU 22 is inputted with a water temperature signal 'Tw' from a water temperature sensor and an opening signal 'TVtheta' from a throttle sensor 21. If water temperature 'Tw' is lower than predetermined temperature 'T1', or 'Tw' is higher than 'T1' and the throttle opening 'TVtheta' exceeds predetermined opening 'theta1', air-fuel ratio control is made to go on according to a theoretical air-fuel ratio. Namely, when the engine 1 is in an idling state in this case, a valve device 18 within a bypass passage 17 formed bypassing a throttle valve 5 is made to open, while said device 18 is made to close in non-idling operation. Also, when 'Tw' is higher than 'T1' and 'TVtheta' is less than 'theta1', the valve device 18 is made to open and a large quantity of intake air is fed to a combustion chamber 9, thereby enabling the engine 1 to be operated on a lean air-fuel ratio.
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