Just had a member with a similar problem and found that it was the upper intake manifold gasket. She sprayed carb cleaner around the base of the manifold (where it meets the lower intake, you can easily see the bolts that hold the upper intake in place - spray around there) and her idle smoothed out, which proved it was a fail gasket that was allowing excessive amounts of air to enter the air stream after the MAF.
Hope this helps!
