Surging throttle from start

[absentmathis]

I've posted about this before and had it in to the dealer multiple times but they can't fix it. When accelerating from a stop or very slow roll there is often an obnoxious throttle surge around 1500-2k rpms. I hold the pedal light and steady which should result in fairly linear acceleration, but a passenger would probably tell you I mashed it for a half second...it's enough to snap everybody's head back to the headrest. Then instantly back to linear feel. The transmission was replaced under warranty last year, they've reset its computer several times to no avail. No codes elsewhere. Engine runs great otherwise. Best I can figure it's a glitch in the throttle. The problem does not occur 100% of the time (which hinders dealer diagnosis) but best I can tell is *more* present after longer highway drives. Any thoughts?

Edit: I forget this forum doesn't have car info, it's an '08 48i.