I don't know the B280F that well, but your description of such huge rpm surging makes me think that the computer is not receiving a good rpm signal. On some other makes I've repaired, a bad high resolution pulse can cause such things. Many makes use a lower res pulse at higher rpm. I'm not sure if Bosch does this. I read that you replaced the crank angle sensor - and it should be fine - but if not, for whatever reason, that may be problem. I know that others have found that damaged tone rings on the flywheel will make for misfires, just how the B280 determines crank angle I don't know, but it should be investigated.
On one of the makes I've had experience with, disconnecting the idle air control valve "calmed" the surging, but the engine could still be felt trying to surge as the ignition timing changed. You might try that. On a scan tool (OBD 1) the rpm signal could be seen jumping up and down in excess to what the engine was actually achieving - and that confirmed the diagnosis.
I hope this helps.
Rhys