I have seen engines fire with just a turn of the key to the start position. You wuld have to a cylinder at the tiop of its compression compression stroke and a spark to occur with the turn of the key. Kind of hard to do with a electronic fuel injection but could be easier to do with the idle twice as high as it should be. I would first look for vacum lieaks. It would probably have to be larger leak like EGR hose into the elbow just before the throttle body. also check the brake booster hose. I bet if you get the idle under control the problem will go away.