The car is a '92 Seville. There is a roughness at idle that becomes
more pronounced with a load such as in Drive or with the AC on. The
higher the engine temp the more pronounced it becomes also.
Interestingly, on increasingly rare occasions, at all temps, it is
barely present at all. There is seemingly no pattern to this variable.
The following parts have been replaced, cleaned, inspected, or tested
per the FSM recently...
ISC motor, plugs, cap, rotor, wires, module, cam position sensor,
pickup coil, EGR valve, fuel filter, fuel pump, PCV valve, injectors,
FPR, vacuum lines, motor mounts, brake booster, and all accessible
electrical connections. The vacuum reserve tank holds vacuum after