Replace the TFI Module (the little box on the distributor that the wires go into). It sounds like it's not making good contact with the distributor. Make sure you do a really good job of cleaning off the old gunk and apply the new grease that should come with the new module. You're going to need a 5.5mm distributor wrench, also. You can usually get those at any auto parts store.
They look like this -
or this -
.
Good luck, Lauren.
You know how to find me if you need more help..