I had the same problem and finaly took it the the dealer.
They replaced the injector, and the EGR valve because it was
stuck open with carbon build up. They replaced the injector because it was "suspect" but I think it was the EGR causing it all and they just mis-diagnosed it and made me pay for it!!!!!!!!!! however, I got a new intake manifold gasket and labor out of the deal for free 'cause they
mis diagnosed it as that first and replaced it with no change in the way it ran.
Hope this helps!