An IAC would not cause a misfire. I would check the plugs/wires, especially the wires. There is no ignition module on the car so don't go and try replacing that. It's likely to be either the plugs, wires, or the coil. Start at the cheapest and work your way up. You can check the condition of the plugs and spray water on the wires in a dark place or at night to see if the wires are still good.
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