Drive off in Open but go too far (9)
I believe the answer is:
overshoot
'go too far' is the definition.
(I've seen this before)
'drive off in open' is the wordplay.
'drive off' becomes 'shoo' (shooing is a kind of driving off).
'in' is an insertion indicator.
'open' becomes 'overt' ('overt' is associated in meaning with 'open'**).
'shoo' put into 'overt' is 'OVERSHOOT'.
'but' is the link.
(Other definitions for overshoot that I've seen before include "Go beyond the mark" , "Go extra distance" , "Fly beyond" , "Taxi too much, perhaps" , "Go beyond the intended target" .)