Why is my friends 93 Oldsmobile Cutlass Ciera dying?

My friend has a 93 Oldsmobile Cutlass Ciera that is dying for no apparent reason. The car will run fine for about 20-30 minutes and then just stall out. If you wait about 10 minutes, it will start back up just fine and run for another 20-30 minutes before doing the same thing over again. I've replaced all the ignition coils and the ignition control module which seems to have given the car a little bit more run time before it stalls. Any ideas?|||crank sensors go bad on those commonly.