Check the connections where the plug wires connect to for rust or corrosion and clean them with a wire brush etc.I'd be treating the fuel system with something like STP or Lucas fuel treatment , then after using up a few tanks of fuel change the fuel filter on it. Also make sure that the charging system connections a the battery , starter , alternator , and engine block ground and all other grounds are good on it too.
Hope that helps and best of luck.By the way even a slightly loose belt can cause more fuel consumption or wheels that aren't balanced properly or sticky brakes or a fuel pressure or fuel regulating valve that isn't working correctly etc.
It might not hurt to have a free scan performed on just in case any error codes exist.