I just got a 1994 S10 Blazer. When i took it home at a stoplight it had a bad idle and it lopes up and down and when it bogs down it will puff a little black smoke. It was getting bad gas mileage also. I took it to jiffy lube and got a fuel cleaning system then changed the fuel and air filter and plugs and wires. This all helped it doesn't smoke as bad and gets about 20mpg but it still has the rough idle and smokes a little. When i start it to warm up in the morning there will be soot on the ground out of the tailpipe. Three plugs on one side were fouled the other three were ok. It doesn't idle so rough when the engine is cold but when it gets warm it starts to do it. It hasn't used any oil and i've drove it over 1,000 miles. I also have to crank it over awhile to get it start sometimes. Please Help!