Internal combustion engine and straddle-type vehicle including the same

An engine includes: an intake passage through which air is guided to a combustion chamber; a first valve disposed in the intake passage; and an ECU that controls the first valve. The ECU includes: a first control section that keeps an opening of the first valve at an opening equal to or smaller than a first opening at least in a portion of an intake stroke of a first cycle; and a second control section that changes the opening of the first valve to a second opening greater than the first opening before end of an intake stroke of a second cycle subsequent to the first cycle, and keeps the opening of the first valve at the second opening at least in a portion of the intake stroke of the second cycle.