1994 Oldsmobile 88 Car running rough

My car has been driving fine until lately it has gotten where it wants to die everytime I stop at a light or stop sign. It even died twice while I was driving and I managed to pull off the road and it started right up. We have changed the plug wires and plugs, checked for vaccum leaks, changed fuel filter and throttle position sensor and are at our witts end. We have had several mechanics tell us if it dies and then startes right up it most likely the computer. The problem is which computer. We have one under the passanger side dash and one under the hood. We have tried to have the problem checked with the tester but it keeps reading "Error" and can't be checked. Please let us know where to go from here.