1991 Oldsmobile 98 engine runs rough

Engine Performance problem
1991 Oldsmobile 98 6 cyl Two Wheel Drive Automatic

My 1991 olds 3800 (112000 mi) misfired last summer. I drove 15 mi home at which time it smoothered out twice for a short time. It runs quite rough. I recently replace plugs and wires - it improved slightly. I then replaced PCV valve, again it improved. It will now idle and I do not have to have my foot on the brake and gas to keep it going. Idle becomes rougher when I put a load on by putting in gear. It will idle and run but still is rough running. It is likened to the sound of a deck of card as you shuffle them. The idle has gone from a rough performance to a sputtering one.

Thank you !

Chuck