problem w/my friend's car (video clip)

my friend has a 93 mustang gt. he hadn't driven it since about a year ago, until yesterday, because of a problem it has. he does turn it on once in a while, though. we don't know what it is. a whole mess of smoke comes out through the exhaust and it stinks. it idles at about 900-1000 rpms. once in a while it does this sort of clunk or popping sound. here's a small video clip. you can hear it at about 21 seconds into the vid http://media.putfile.com/inside-wiltons-car
any ideas? thanks