i have a dodge intrepid 3.5 a week ago i parked it in the driveway. went out the next morning and it would not start. it would crank over but no spark. changed the crank sensor and no start. changed the cam senor and it started. now it is shutting down at different times some times at highway speed some times coming to a stop sometimes just after starting and putting into gear/ no check engine light and no codes it will go days with out dieing. car has 125000 miles any ideas.