My 85 Blazer is running a little wierd. When I first start it up, it idle's very high and is kicking out black smoke all over. This is rather nice when I'm parked next to another vehicle as they now have a big black carbon mark on their vehicle. After a few minutes of running it, it will drop down to normal. I have tried to dial down my idle, but then after it warms up, it's too low and stalls. Any ideas?