Mystery solved. See pics. The throttle plate was smacked by the loose bolt banging around, and bent it at the bottom corner hinge point, and knocked that small throttle plate spring stud off/out from underneath the plate. It left that plate a bit twisted and dented and bulged at the hinge, which restricted movement of the plate and linkage assembly.
Where can I buy a replacement plate? (I can tig weld and straighten this one if I have to, using good hinge side as a reference, but would rather not.)
Thank you all for taking a look.