Have a 96 502 MPI and my coil keeps going out when the boat is idling, I have new plug wires, dist. cap, rotor button and even swapped the the ignition relay. The distributor is less than a year old so I have not swapped the module yet but that is the only other thing I can think of, any ideas?

Check actual voltage to the coil while it's idling. It sounds like you may be overheating it due to low voltage. The module should not be able to kill a coil since it's switching voltage is so low. Also make sure you have a good ground at the coil for the same reason.

The Delco EST distributor uses variable dwell to control coil current (and temp). You can use a common dwell meter to see if it is doing what it is supposed to. At idle, you should have less than 15 degrees of dwell. At just over a thousand RPM, you should see in increase to about 23 degrees dwell.

Dave