my ls did this, it was a vacuum leak at the intake mani. it was the main hose coming of the top of intake mani like in the center, im drawing a blank on what its called. i fixed the leak and it runs great now-

 

just get a whole new intake manny with all sensors

 

lol ^ ,also check if your intake manifold is bolted on tight. had this happen before.

 

yea definatily one of the sensor's on the TB if you pull your intake off thare are holes in the inner TB put your finger over each hole one at a time and that could possibly tell you which sensor..idk i had my boy show me that trick about 3 year's ago.but then again it could be a number of thing's like listed above.