Unplug any major sensor and it cuts the feed from ALL. So you kill the ECT the ATS the o2, etc the ECT ignores all of them (adaptive fuel off). Most early obd1 systems don't feed filler values like obd2 and one bad value can kill the whole data stream because it can't "fall back. Codes also don't always light the cell so many times you have to manually check them to find them, and some never set to memory. Its like a TI82 not a PC.
The gist being "unplug to test" is really bunk on obd1. If you are backfiring it also can be ignition, fuel, and both aren't monitored. But to rule out 02 you need an equivelant of the brick tester or a multimeter. Then the other sensors need to be checked too. 02 sensors only really go bad in specific cases (coolant in exhaust, gas flood, or super lean) so another preexisting issue won't be fixed even if it is bad.
Just my 2 cents
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