If the management light isn't on I don't think you will extract a code from it. Misfiring is common fault on cossies usually simple to fix. Most of the time it relates to phase and crank sensor, a weak spark causes loads of problems. I would disconnect every plug on the engine loom and clean them up and then double check phase and crank sensor gaps and position. After this cap, arm, coil and leads and plugs. But also check connections under dash by ecu as a couple of relays are under there, one for ignition other for fuel pump. Also have a look see if any play in distributor shaft, as this can play havoc on sensor gaps.