1998 Chevy Monte Carlo Rough/hard start/black smoke/rough i

This car has the 3.1l v6 and you have to push the accelerater to start it then there is black smoke out the exhaust, heavy at first then just light black smoke. Once I get up to speed it seems to run fine but when stopped it runs rough again. Additionally the service engine light will come on as well as the abs light then sometimes go out. It seems as though there is low vaccuum too.