I had a similar problem on a truck of mine. Come to find out there was a pin head sized hole in the gasket between the intake manifold and the TB. It was sucking air in the wrong places, long story short, I replaced the gasket and it ran perfect again. Good luck dude!

 

fuel injected engines are amazingly sensitive to the little details

 

ok if you have a o/r h pipe you need to shut off the rear o2s with a tune or get simulators