you may have moved the idle aswell when washing, it is just here:
but this wouldn't make it suddenly race* as an incorrect setting on the idle would just keep it at high revs in neutral; or stop it starting at all. Plus its one of the easiest things to knock when cleaning.
I still say its a throttle/cable issue, but its also something worth checking. If you are worried at all though the best bet is probably get it checked over by a dealer.
*unless the automatic choke was allowing it to happen, I don't know for sure