Backfire up thru engine and hesitation

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Wondering what causes this? In the morning when I first drive the car, I get a backfire some where it sound thru the top on the engine. It isnt loud and after I get a certain hesitation. It goes away rather quickly after a block or so of driving. But it is now starting to drive me mad since I am now driving the car a bit more and back to fixing it up. Any ideas? I'll run codes in the AM...