Is this what you are doing, you turn the key till it cranks, then once the engine catches and fires you back off a little so the starter stops turning and the engine stays running. If you let go of the key it dies? If so it sounds like a bad ignition switch to me. I've never changed one in a Honda so I can't help you there but what I'm talking about is the actual switch, not the ignition lock itself. When you turn the key in the lock it activates a switch, and I think the switch is what is bad. Hope this helps.