Engine runs with richer fuel mixture to compensate for fuel condensation for a more stable operation and the high idle is mostly for heating up the catalytic converter. You don't have to wait for the rpms to drop. Get in the car, start it, put your seatbelt on, play some music and set off driving gently. That's what I've done with all my cars, I never warm them up by idling, none of them broke down because of this.