the shaking at startup could be bad or incorrectly installed o2s. theyre very sensitive so if you bumped them or dropped them, they could be broken. pre-cat o2s help regulate afrs, without them your car wont be happy at all, esp when its not warmed up. Its not a critical failure like a water pump, but you want to get it taken care of.
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Motiv Port Fuel/Meisterschaft Race/Berk Resonated/ER CP/Synapse/VRSF FMIC/Rob Beck PCV Valve + Cap/ST Coilovers/M3 FCA + Tension Rods/M3 Subframe Bushings/M3 FSB/AA Strutbrace/DINAN Camber Plates/Apex ARC-8/Project Kics/VAC Hubs/Rogue Transmission Mounts/Alpina TCU Flash/Icarbon/#Tee CF Stuff/Kerscher/BMW Performance