Well, based on a quick read of those links a bad TB drive motor is possible. I've not experienced or recall hearing of any G-man having this happen from Grooving a DBW TB.
I do think it's possible you cut the Groove too close to the closed throttle position. IF it turns out your TB is toast, here's what I'd do. First install a replacement TB. With no dark stain to go by, I'd just install the new TB, and drive it till it is settled in- there may be a learning period for it and the ECU to mesh properly. Once it's OK, I'd scan the ECU at warmed up engine idle RPM's. To see the throttle angle or percentage at that hot idle rpm.
Then, w/ warmed up engine, key on engine off, (KOEO) see if you can position the plate to that position, by hand, and mark the position. You would need a helper to watch the dongle or other scan device, to call out when it's at the idle position. I had to do this once a few years back, on a DBW Chevy Avalanche. Before trying to move the plate by hand have the air duct off, and have someone turn the key from off to on without starting. You will likely see the motor move the plate when the key is first turned on. So watch for this first before sticking fingers in there. It was a bit tricky on that truck. It won't run of course w/ the air duct off.
BTW, did you try inserting a business card against the plate, to see how close it would be to where you actually cut? I had concern of the Groove's location seeing your pic, my concern was of abnormal high engine idle RPM. I've both Grooved and handled a few GM DBW TB's, never had an issue of drive failure or any sign of difficulty from manually moving the plate.
Only other immediate idea is re: the MAF, and check all electrical connectors. And-did you Check your work w/ a flashlight? You didn't mention if the bit broke into the epoxy, but if it did, and if you had to remove any epoxy to get that pipe to fit... a vacuum leak in the TB could also cause this.
I'll have my phone on again tomorrow, Greg!
Tracy G