I noticed this on my way home from work last night. I was in fourth gear accelerating and when the tach hit 3k the turbo started surging with the throttle held steady. It didn't stop until I let off the throttle. Played around with it the rest of the trip home and every time I hit 3k the turbo would surge.I do have a p0420 code that will be getting looked at tomorrow, is this related? Has anyone else experienced this?