When the level of the low frequency components is larger than a predetermined value, it is regarded that the noise is generated due to unstable combustion during the low load operation or the spike noise is generated due to corona discharge of a spark plug 16, and {HEAD ~ the determination} of {TAIL ~ the occurrence} of knocking is prevented 
When the level of the low frequency components is larger than a predetermined value , it is regarded that the noise is generated due to unstable combustion during the low load operation or the spike noise is generated due to corona discharge of a spark plug 16 , and { HEAD ~ the determination } of { TAIL ~ the occurrence } of knocking is prevented
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