a bad o2 will lead to sputtering and an uneasy, lurching idle, especially when cold. My car is in right now with a bad lambda o2, it didnt seem to lose much power though, and no limp modes etc. Mine is hopefullt going to get taken care of under cpo, but if not the dealer will rob you blind on them, 800ish bucks to replace one. Tischer sells them for around 180 i believe, and installation isnt very difficult from a mechanical standpoint.
E88 FBO N54 Alpinweiss/Coral Red/Meisterschaft Race/Berk Resonated/Macht Schnell 3"/ER CP/Synapse/VRSF FMIC/FFTEC LPFP/HFS-4 DO Stainless Lines/BMS DCI/BMS Thermostat Delete/Rob Beck PCV Valve + Cap/BMS OCC/PTF E50/ST Coilovers/M3 Front Control Arms + Tension Rods/M3 Subframe Bushings/M3 FSB/DINAN Camber Plates/Apex ARC-8/Project Kics/Macht Schnell Studs/VAC Hubs/Rogue Transmission Mounts/Alpina TCU Flash/Icarbon/Kerscher/BMW Performance