We get black stains on the driveway from the condensation blowing/dripping out of the exhaust pipes when it is cold here. I don't know what your weather conditions are like now, but here in the winter, when we start up our cars (and warm them up for a few minutes) there is cloud of steam that rises from the warm exhaust- as the condensation that settles in the exhaust is burned off. There is steam and dripping until it's burned away, and it leaves little black spots of the driveway, since the moisture carries carbon deposits out the tailpipe. With good plugs and wires, good cap and rotor, etc. in a gas model, it may be a similar situation. Good luck.