Tonight I did switch the coil packs on #5 and #6 as suggested and that made no difference, and I put new plugs in already, so I'm thinking it's very likely the primary wire or the injector. Haven't had time to check those out yet.

Checking further with the OBD reader (which is pretty informative, now that I'm starting to understand what it's telling me) I found that the first O2 sensor was oscillating between about .75 volts and .1 volts--a bit lower than described in the FAQ, but pretty close. The second one, though, read at a flat zero--I'm assuming that's the one behind the catalytic converter.

So I'm convinced the O2 sensors aren't the immediate cause of my rough idle . . . and I just read a note on another thread from somebody who said his car's running fine with the back sensor dead. But I wonder if (assuming it really is dead) replacing it would be a good idea anyway.

Thanks again--JG