Runs engine very swiftly when starting? (4)

I believe the answer is:

revs

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'runs engine very swiftly when starting?' is the definition.
I can't tell whether this definition defines the answer.

'runs engine very swiftly when starting?' is the wordplay.
'when starting?' suggests taking the first letters.
The initial letters of 'runs engine very swiftly' is 'REVS'.

Can you help me to learn more?

(Other definitions for revs that I've seen before include "Units of engine speed (abbr)" , "Rotations of a motor, in short" .)

I've seen this clue in The Times.

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