Fuel trims are somewhat lean, but not terrible. Normal range is up to 10%. So maybe a little vacuum leak someplace, or dirty injectors, or combination. The PCV valve should probably be changed if not already done, but that tends to produce a bigger leak when it tears.
For the smoke test, you need to keep the butterfly valve in the throttle body propped open or you’ll only test up to the throttle body.
620 idle speed is not really too low. As i recall, mine is about the same once warmed up, but i don’t notice shudder or surging.
Reading through the posts again, your voltages look low. 12.2v seems pretty low at rest. I believe you want something around 12.6v engine off and everything shut down, and you should see something around 14v+ when running. The electronics stay on for a surprisingly long time, so testing when off I suggest popping the hood and leaving it open for a good 10 minutes before testing (and leave the key someplace far enough away that it doesn’t energize any systems when you approach).