1988 Chevy Celebrity Carbon bits spit from muffler.

OK, I don't drive this car too much, but lately when I go to start it, it (putts)- barly starts, - and when it turns over, I see a little bit of white smoke- for a few seconds, - then small bits of black carbon spit out form the muffler, along with a smell of gas. Now this has happened four times, and does not happen every time it starts, but once in awhile it does, - but for a few seconds. Now, it has been runing rough, and stalls at idel. I'm thinking that the egr valve needs to be cleaned, or replaced. Can anybody tell me if this is the case?- I would like some help. Many thanks!