Buick Regal Engine Rich

Will Running My Buick 3.8 Liter Engine To Rich, Cause Much Problems Later? My Gas Mileage Is A Little Worst I Think? Are There Other Things...

This Vehicle Idles Down And Up Then Dies, It Is Blowing Black Smoke, And Has Killed It's Converter

Problem - Car Is Running Very Rich, No Smoke But Strong Order Of Fuel At Tail Pipe. Loss Of Power, Car Shakes At 40 Mph Or 1900 - 2000 Rpm...