hey . could do with some help

Just took the impreza out for a drive, I gave it a bit of a boot but nothing stupid but when i slowed down and put the throttle on it started jerking and popping, almost like a misfire?
But when the boost kicks back in its fine! it just runs really boggy when in low revs ei driving it through a town.
Ive had a quick check to see if the leads into the pack are ok and they look fine and its too dark now to check everything.
Has anyone had this situation?
Im wondering if its has something to do with the spark plugs or lamda sensor?
any help would be great