car starts and runs stops when you let go of key

:shock: i bought this 95 accord ex for my son today its a hot day he drove it for awhile and then later when he went to start it to show his girl friend lol the car started and when he let go of the key it quit aslong as you hold the key on it runs fine hes looking at me like i betrayed him please help what part of the ignition system am i to replace