96sc2 wontstart bad mpg plugcarbonfouled

we got this car a couple months back. the fuel econ. was never good. one day it would not start until i put the gas to the floor. it ran at a fast idel 1200rpm all the time and it would smoke on start up. it got worse 2 weeks later it would barley start and run the smoke and fumes were real bad . Autozone recovered code 1406 EGR circuit? and multiple cylender misfire. I think the colant gauge read cold (maybe) i didn't drive this car much. the spark plugs were carbon fouled(fine black powder) the tail pipe showed the same. When the car would run i had good engine power I swaped the EGR valve (25.00 bucks) salvage that didn't work. I read some place about the colant temp. sensor? that was the fix.(14.50)at saturn. start up is great and ecomony is about 25 mpg (est) 1.9 twin cam the sensor is on the head driver side by the EGR valve also i think the trans is shifting better (maybe) thanks hope this helps willie