A throttle body injector that is blocked-opened is a possibility. THere are 2. Peeking visually into the TBI can provide a clue, or tricking the wiring to drive one injector at a time .... I doubt a false O2 reading can have such an effect...specially since O2 control happens only after engine has warmed up...unless that is the case.
www.avigex.ca/xport/injectors31_1.jpg
www.avigex.ca/xport/injectors31_2.jpg
www.avigex.ca/xport/fuelcontrol31.jpg
THe blockage can be mechanical or electrical (shorted grounding transistor).