Hook up a vacuum gauge when you are done to see if it returned to normal (18-20" of Hg).
Had a 94 firebird come in with the opposite symptom yours had. It kept adjusting lean in closed loop on one side until it started missing out, because the BAD o2 sensor stayed stuck at .56V, and it RELENTLESSLY believed the o2 sensor without setting any code for it. Replaced the sensor, and cured it. I seriously wonder about your O2 sensor wiring, but we still had a bad vacuum reading, which trumps the electrical with a physical problem. A shorted-to-ground O2 sensor harness may be your other problem. There should be a .45V reference sent from the computer to the O2 sensor's output signal. Unplug the O2 sensor and look for that exact voltage +/- .05V. If it is out of range, begin the hunt for a bad ground or short to ground or open circuit.
The latest beta version of EEHACK 4.8.2 lets you reset the fuel trims, which is a great tool for finding the truth about O2 sensors. Reset, and see if it smoothes out.
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