Thank's Goats. I switched the light grey connector to the ignition module in the forward position and the dark grey connector to the module in the rear position.
Uncertain if this means a connector was not secure, but after the switch the rough idle and vibrations settled down, and the rich exhaust smell diminished. Exhaust manifold temps with IR gun seem to indicate all cylinders throwing heat, though rear bank (1-2-3) appears to be hotter. (Due to angle of curvaceous manifold pipes, readings seem to vary with laser-spotter placement.) No codes before, and no codes now. After a thirty minute in-town test drive, motor seems to have good power on acceleration, but during hot idle at stop lights there is spotty roughness. Spark plugs were changed for first time about 12k ago, but original coils have never been replaced. I'll switch back the connectors and see what happens. Goats, you mentioned that when one of the two ignition modules fails it usually shows in one of three cylinders of that assigned bank. Will that cylinder show no heat or simply less heat than the other two cylinders in the bank?
1995 164 LS 5 speed 78K
owned since new