Weak/no idle and sometimes will not start

The bus drives for about five minutes and then the idle disappears and the engine shuts off when I come to a stop and then it will not start back up. The entire engine compartment in the back seem to be pretty hot after it shuts off. I have replaced the distributor cap, wires, spark plugs, and ignition coil and timed the distributor to get rid of all the back fire. Cannot figure out what is going on. Please help.