Do not press it all the way or you will stand up, which makes you go slower. You can reach maximum speed on scooters and motorcycles by pressing Up slightly on the Analog-pad to duck your head. Make sure to hit the doors off of the back this should make it easier. | Submitted by GrantandAlex The person should get out and it should count as a rescue. While doing the Ambulance Rescue, when you go to pick up a person,(usually works in the back doors) right before they are about to get in, get out of the ambulance and get right back in.
Watch mission cutscenes at Clymenus Suite - 100% Completion Grand Theft Auto: Vice City reference.