Sierra had foul emissions removed with absorber (7)
I believe the answer is:
sponged
'foul emissions removed with absorber' is the definition.
I can't tell whether this defines the answer.
'sierra' is the wordplay.
I cannot quite see how this works, but
'sierra' could be 's' (phonetic alphabet: alpha, bravo, charlie etc.) and 's' is present in the answer.
The remaining letters 'ponged' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'had' acts as a link.
Can you help me to learn more?
(Another definition for sponged that I've seen is " Cadged".)