Sometimes when i start my 87 300d it has a rough idle. It will run rough, idle speeds up to over 1k, and blows black smoke. I can turn if off and restart and most times it idles smoothly. At times that the restart doesn't work I can drive it 5 or 6 miles and it idles smooth again. The power is always good,rough idle or not. The injectors are good.Any idea what would cause this problem?