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/Other stuff...652WHP
F30 N55 XDrive EBII