99 Merc 350 MPI is sometimes quitting while running at 1500rpm. Now it Will not start, just clicks the starter relay. Let it alone and sometimes it will start. Batteries are up. Can't find any wires loose or broken. Engine alarms still work before you turn the key to start and then it will just click. The starboard engine still starts and runs fine. Where do I look first?? Why would it quit running with no alarms sounding??