Crossword Genius

Adjust an instrument or vehicle (4,2)

Ross

I believe the answer is:

tune up

(Other definitions for tune up that I've seen before include "This should improve engine performance" , "Adjust for better functioning (car); for better sound (musical instrument)" , "Prepare for performance" , "make corrections to pitch" , "Work on engine" .)

I've seen this clue in The Guardian.
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