Also, it could be a stick throttle plate, or the throttle body could be obstructed. Spray a little carb cleaner in there, and get in there as far as you can with a rag and wipe it clean.
Also, make sure that all hoses that go to the air box are secured, and make sure that there are no cracks or leaks in them. Your focus should be around the throttle body itself, and the air box. If the MAF sensor was replaced, then perhaps that's not the problem, unless your dealer didn't really replace it.