2004 s60r backfire & engine miss

[royboy]

just got my dream car 2004 s60r awd 6 speed how is this thing supose to run? it backfires in between shifts and lags in power when i get on it is misses and then it goes i checked vacume lines could it be the mass air flow sen? or a turbo boost silinoid what else can i check? it was throwing a po299 code but i cleared it last week and it has not come back on after 200 miles (no cel on)