Had similar issue, the following points sorted my standard B7 RS4:
1. Replaced fuel filter located just before the O/S rear wheel.
2. Had sparkplugs replaced.
3. Removed seized under air box solenoid and auxiliary flap (it was seized shut restricting airflow, also getting better mpg now).
4. Replaced standard paper air filter for K & N direct replacement in standard airbox.
5. Replaced cruse control module located on the clutch peddle.
6. Disconnected vacuum unit on rear exhaust (standard Audi RS exhaust) and sealed vacuum pipes as N/S seized shut, both fixed in open position, (also sounds much better).
7. Go's with out saying better off using a minimum 97 RON Super Unleaded, my preferences are Shell V-Power (which I think is 98 RON) & BP Ultimate (which I think is 97 RON).
I had the Standard B7 RS4 on a rolling road when I first bought the car it made 324bhp (poor & disappointed spring to mind) after the above items were undertaken it developed 390bhp running on BP Ultimate, no throttle hesitancy, clean free revving.
As a foot note I had the RS4 to a couple of 'Audi Specialists' who automatically presumed it was coked up (common problem), I didn't fancy having my engine pulled apart after just 41,000 miles, so went a different route checking the basics leaving the decoke as the last option.
Most of the above points are DIY, I had the sparkplugs changed by Audi as an extra during a routine service.
Hope this helps as I know how annoying the throttle hesitancy/misfire can be, spoiling the RS driving experience.
