It sounds like you damaged something with this bump.
I'm guessing the inner wheel liner that hangs under the engine a bit (even if you removed the under-tray) got dislodged and is maybe pushed onto the aux' belt.
The aux' belt turns the alternator, as well as the air con'. Steering is electric on all Stilos as far as I know.. but your aux belt could also be powering the steering if your steering is hydraulic... so any problem with the belt would affect alternator, air and (possibly) the steering pump.
So, take the front wheel off and remove the inner wheel liner to see what's happened. I suspect the belt may be frayed, if something got caught in it. If the belt is frayed or slipping it will smell of rubber, whine and soon break, so change it.
Also check the tensioner didn't get damaged. If it's leaving the belt loose, see above. If it's jammed "tighter" then that's no good for the alternator bearings or the belt, or the aircon pump bearings, so fix it.
High idle speed suggests the engine is fighting some resistance, since the ECU has an anti-stall program and is trying to keep the engine from cutting out.
Ralf S.
