Yeah, mine does it. I have quite figured out the magic combination for reproducing it, but I know exactly what you're talking about.
I've done nothing to fix it, because I don't care at all lol.
It's basically impossible to powder the throttle body. You definitely have to take it apart (there's motor and plastic in it) then it has to be re-assembled after. We were going to try with one, but gave up, and threw that TB away. lol
Nope, these cars are all torque request based, not MAF based. Changes in airflow will adapt automatically. This is not an opinion, it's fact. The way the ECU in these cars behave is unlike a lot of other cars, likely the cars you've worked on in the past.
https://www.supramkv.com/threads/1000hp-evolution-of-speed-turbo-kit-billet-manifold-bottom-mount-xona-11569-8000.19690/page-2#post-319835
Included is this sale ?? $7000.