1992 BMW 520 hesitation

Check ingnition components they may have gotten wet also see if there is water in air cleaner.

Often when you get bad ignition wires wet it will run badly. Water my have gotten into the electrical system somewhere, but if that is all it is it should get better the next time you get it real hot because the water will evaporate.

Is there a check engine light on?

The secondary air injection intake was placed in an unfortunate location on those models, when they encountered deep water there was a possibility of water going into the engine. There are no spark plug "wires" as these engines utilize coil over type ignition and it is once again possible to have a coil failure (or coils) The electronic sophistication of the newer BMW cars is such that they require diagnostic equipment that is used at the dealership and some of the higher end independent repair facilities, you may have to seek out one of them in your neighborhood in order to resolve the issue(s).