PURPOSE: To commonly use parts and to perform simple and accurate purge of vaporized fuel and diagnosis of a trouble of EGR by aiming at comparative similarity of a purge operation region of vaporized fuel to an EGR operation region.
CONSTITUTION: The opening end on the throttle chamber 2 side of a first signal negative pressure passage 28 through which the pressure chamber of a purge on-off valve 26 and a throttle chamber 2 are interconnected is arranged in a position situated downstream from a throttle valve 4 and a three-way valve 29 is located. The opening end on the throttle chamber 2 side of the second signal negative pressure passage 33 through which the pressure chamber 32a of an EGR device 32 and the throttle chamber 2 are interconnected is arranged in a position where it is communicated with a position situated downstream from the throttle valve 4 when the opening of the throttle valve 4 is further increased. Further, a portion between the three-way valve 29 of the signal negative pressure passage 28 and a purge cut valve 26 and the second signal negative pressure passage 33 are interconnected through a passage 35 in which a one-way valve 34 is located. The occurrence of abnormality of a device is diagnosed according to opening and closing of the three-way valve 29 and the presence of EGR.
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