What would make a 1988 trooper ii idle rough?

Ours was simple... as in 95% of ALL car problems. Usually just hard to determine what 'exactly' is wrong in the first place. New plugs made ours run 1000% better. Wires didn't help, but if you're replacing plugs, especially 'old' plugs, do the wires too. Check and clean the cap and rotor if any. The final problem was to get a new Cat. Converter and weld it on. (Light was coming on intermittently) Dokter Denney