Why does my car idle rough and misfire when idle, cant be cat i changed that

Preventive maintenance is key to the survival of any vehicle. Have you had regular tune ups?, what type of fuel are you using?, has anyone did any recent work on this vehicle?, how long has this problem existed?, are all the fluids clean and full?, Is there a check engine light on? if so a code has been set, get the vehicle checked, are you a DIY person? what's the status of your fuel filter? What was wrong with your catalytic converter? I have older vehicles also so I know they need a bit more care, and the right type of care, How many miles are on this vehicle, u know Hondas last a long time, just check out the highways. let me know the answers to these questions. thanks I had a 1992 Honda and it is still running great