I just went and checked on the ground with an ohmmeter to be sure. It measured .01 ohms between that ground wire and the manifold, and the same from the manifold to the negative battery cable.
I haven't done much on the car for a few days. I've been a little discouraged about it to say the least.
I did notice the a/c compressor making some intermittent squealing noise from the pulley while idling. I wonder if the bearings are going bad and causing an extra load intermittently, resulting in an unstable idle? Or does that just sound totally crazy?
Edit to add: I hear the squeal from the a/c compressor/belt at startup too (very loudly). It's been doing that for a while, but just now was able to pin it down the the a/c compressor while hearing it at idle.