The OP isn't trying to rev the nuts off his engine,
Soryy, but can't agree with that. He is pressing the loud pedal to the floor, thereby requesting the engine provide maximum airflow, maximum fueling, and therefore maximum revs. Just because modern engines have "rev-limiters" and the like, it still doesn't mean it is safe, or advisable to rev a car to high revs without any load on the engine. This was fully explained, and painfully (to the owner) demonstrated to me by a Ferrari engine technician at Grey Paul.
he's just concerned that the throttle response isn't what it should be and is testing by comparing a short 'foot to the floor' blip against another car... during which short time it wont over-rev anyway. Not the most scientific test but a decent benchmark nonetheless.. and with a 750rpm difference I'd say there's something not quite right there.
Like I said, "foot to floor", or indeed any "blipping" of throttle is a very bad idea on a turbo engine. How would you like to be trussed up naked like a chicken, and then spun around at 180,000 rpm on your bare butt cheeks without any lubricant?
If the OP is concerned about actual throttle response, then his method certainly aint an appropriate method. VAS505*, or VAG-COM, and/or a RR session would help/tell.
Regarding the difference between the TT and the GTI - well do they have identical engine maps? Even if they both have "OEM" maps, there can still be differences, and the manufacturers are known to release revisions to standard maps, which can noticeably alter many "traits". On my RS, the revised engine map dramatically altered mid-range throttle response, but also altered the operation of the exhaust valves - so going back to the specific concern of the OP, this perceived difference may actually be perfectly OK.
In days gone by disconnecting the battery for a while caused the throttle body alignment to reset.. not sure if that applies to anything after the MK4 though.
I'm sure that on all the later Bosch MED ECUs, the throttle body was re-aligned every time your turn on the ignition. I can hear, and feel the throttle body doing just that on both the GTI and the RS. So I doubt the battery method would add anything further - though, providing you have the audio sec code, there would be nothing to loose by trying.
