1997 olds Achieva repeated 02 sensor failures

Is that a Quad 4? If so then you need the coil housing most likely. It acts as the wires. Also check the fuel pressure regulator for a ruptured diaphram. That will dump raw fuel into the intake. There are many things that it could be, try those and get back to me

Let's start from the root(s).
Black smoke is an indication of excessive fuel consumption. A leaking fuel injector, dirty air cleaner element, like jack have said earlier, a defective fuel pressure regulator, or defective fuel control sensor could cause this. You car is equipped with a catalytic converter; the rich mixture may cause a strong rotten egg smell

Your first question was to remove the O2 sensor to solve the problem.
The PCM monitors the activity of the converter by comparing the signals of HO2s located at the front of the converter with the signals from HO2s located at the rear. If the sensor outputs are the same, the converter is not working properly and the malfunction indicator lamp (MIL) on the dash will light.
Some mechanics can just replace the second HO2s because the computer pointed finger at it.
For me, the second oxygen sensor is telling your computer the truth about what is going on in your combustion chamber that may have cause the converter not to work as it should. Check your converter.
Converter is normally trouble free emission control device, but two thing things can damage it:
One is leaded gasoline, I'm sure you do not use that so I do not need to go in details.
The second is overheating. If raw fuel enters the exhaust because of a fouled spark plug or other problem, the temperature of the converter quickly increases. The heat can melt the ceramic honeycomb or pellets inside, causing damage to the to the exhaust valves due to the excess heat.

Let's come back to fuel regulator.
A fuel pressure regulator controls the amount of pressure in the system. Mechanical fuel pumps often contain built-in pressure regulators. However in vehicles with electrical fuel pumps, the fuel regulator is installed in the fuel system between the fuel pump and the fuel distributor.
If you do not find it, let an ASE technician take care of this problem.

On the top of the engine there is a plate with 4 bolts holding it down. Remove them and pull the plate off. There are 4 boots that go over the plugs and on to the coil housing. The coil housing is the large white thing with the coils attached to it. Replace the boots at the same tiome as the coil housing.

Picture below

The best way to determine if a catalytic converter is working is to check the quality of the exhaust. This done with a four-gas exhaust analyzer. The result of this test should show low emission levels if the converter is working properly
Another way to test a converter is to use a hand-held digital pyrometer. An electronic device that measure heat.
But do not quick condemn the converter because it needs a steady supply of oxygen from the air pump. A bad pump, faulty diverter valve or control valve, leaky air connection, or faulty computer control over the air injection system could be preventing the needed oxygen from reaching the converter.