Hissing from rear, loss of power.. micra 2004

Hi All,
At a loss here and hoping some of you clever lot can help clarify this issue I'm having.

So I have an engine fault code of P0171. There is a hissing from the rear of the car that gets louder with acceleration. The car won't go much over 2500rpm before it starts jerking and a loss of power is very noticeable.
Now it starts absolutely fine, there are no issues with fluid levels, no leaks or puddles to speak of and it seems to idle just fine.
Does anyone have an idea or too as to what this might be? Fuel pump?
Many Thanks in advance!
Neil
 
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