1990 Chevy Corsica Engine runing rough

There are 3 ignition coils, each coil sends spark to 2 plugs. They are located on the lower front of the motor, you can follow the spark plug wires down to them. The first coil controls plugs 1 + 4, the second controls plugs 6 + 3, the thrid controls plugs 2 + 5. When the car is in this rough running mode, you can find out which cylinder is missing buy pulling off each plug wire, one at a time, when you come to the plug wire that dose not effect the engine, thats the one thats not firing. You can take the coil off, there are two small bolts, size 5.5mm, or 6.5mm. You can take them to your local auto parts store and they can test them, and they run about $30 for each coil.