I suspect the reason the throttle is too sensitive and difficult to modulate at low RPMs is that the throttle body I’m using is too large. The symptom is that I have difficulty letting out the clutch from a standstill without either stalling the engine or sending the RPMs too high. When I blip the throttle in neutral only a couple millimeters of pedal travel send the engine to redline.

There is a relationship between horsepower and airflow described by the following formula:
Air flow (CFM) = (Horsepower × 0.625) × 1.1104

Under the best circumstances my engine will put out 350 hp which only requires about 243 cfm of airflow. Accufab rated the 80mm throttle body I’m using at 1150 cfm of airflow, so at about 1/5 the possible airflow of my throttle body, I’m at the maximum horsepower of my engine. The remaining 4/5’ths of the throttle opening won’t affect horsepower.

I replaced the throttle body with a 65mm part, the smallest in the configuration I’m using, which is still able to flow enough air for over 600 hp. But it should make the throttle easier to modulate. Now, in neutral, the throttle feels less sensitive but I won’t know if it’s helped until I take the car out again.

The solid engine mounts had too much NVH so I swapped them to Audi RS4 mounts, the hardest rubber mounts for the Audi engine. I used RS4 mounts in my 325 hp S4 and the engine felt very locked down compared to the OEM mounts.

I live on a blind corner, on a busy arterial so Sunday mornings are my best opportunity to take out the car when I don’t know how the throttle is going to respond. So that will be my next opportunity to evaluate the changes.