Ambush fib in audible weight (3,2,4)
I believe the answer is:
lie in wait
'ambush' is the definition.
(I've seen this in another clue)
'fib in audible weight' is the wordplay.
'fib' becomes 'lie' (I've seen this before).
'audible' indicates a 'sounds like' (homophone) clue.
'weight' sounds like 'wait'.
'lie'+'in'+'wait'='LIE IN WAIT'
(Other definitions for lie in wait that I've seen before include "Plan to attack" , "remain hidden while preparing to attack" , "Prepare to attack" , "Plan for ambush" , "Bide time" .)