also: からふかし
noun
engine idling; revving in neutral
Refers to running an engine without engaging the transmission, often with the accelerator pressed. Common in automotive contexts.
信号待ちで空ぶかしをするのは近所迷惑だ。
Revving the engine while waiting at a traffic light bothers the neighbors.
エンジンの空ぶかしは燃費を悪くする。
Idling the engine worsens fuel efficiency.
Alternate spelling using 吹かす; also read からふかし.
Alternate reading for 空吹かし; less common than からぶかし.
アイドリング is the more common loanword for 'idling' in everyday speech, while 空ぶかし specifically implies revving the engine without load.
Compound of 空 (から, 'empty') and 吹かし (ふかし, nominalized form of 吹かす 'to blow/rev'). Literally 'empty revving'.