Truck rough idle po300 multiple misfire code

Last year put in new catalytic converter with exhaust which is still 2 ft short on pipe need to put it on replaced plugs,wires new distributor new cap and rotor new engine coil but the truck still has a rough idle when I push in the clutch it stops idling hard goes to normal idle and the po300 code is still in computer after replacing all those parts if I am not mistaking the 98 chevy 4.3 vortec v6 motor has 4 o2 sensors bit one of my sesors is not plugged in the one before my catalytic converter. Have to install new connection looks like it was ripped off on the vehicle side.the connection on o2 sensor is still there would that cause a rough idle.having an o2 sensor not plugged in.