Petrol with lead in pump’s rapid air intake? (4)
I believe the answer is:
gasp
'rapid air intake?' is the definition.
'petrol with lead in pump's' is the wordplay.
'petrol' becomes 'gas' ('gas' can be a synonym of 'petrol').
'with' is a charade indicator (letters next to each other).
'lead in' says to take the initial letters.
The first letter of 'pumps' is 'p'.
'gas'+'p'='GASP'
(Other definitions for gasp that I've seen before include "Draw breath sharply" , "Puff, struggle for breath" , "Gaps in struggle for breath" , "Say "ah"" , "Show amazement" .)