Saab 900 se missfireing

If you have plug wires you have a naturally aspirated Saab (non-turbo). The entire ignition system must be checked. First, replace the cap and rotor. They are wear/maintenance parts, are cheap, and can be gotten at most auto parts stores (even for Saab). Next, if the high tension leads (plug wires) had cracks and that is why you taped them up, they MUST be replaced. Mere electrical tape will not prevent voltage leakage through these cracks. Make absolutely certain the plugs are resistor and of the proper specs for your model year and engine and that are gapped dead on to spec. Another common wear part is the cam position sensor (a Hall effect sensor that tells the ECU what position the cams are in). You did not mention whether the CEL light is on or whether you retrieved any codes from the OBD port. Go to Autozone or Advance Auto and let them put a code reader on the port to see if you have any active and stored codes (this is free). Finally, a crankshaft position sensor (crank angle sensor) failure could be imminent. This is a known failure part as well.