Hello, I recently bought a 1998 S90 for $4000 from a small dealer near Detriot. The car, as expected, had some problems, but most of them were pretty minor. The one major problem is that the engine idles quite roughly. Once the car begins moving at any sort of speeds the roughness disappears. The check engine light is on and in low speeds the exhaust puts out more smoke than it seems like it should. I also recently changed the spark plugs and they all looked like normal wear except for the first cylinder which was black and looked as if it was recieving too rich of a mixture. If anyone has an idea of what might be wrong i would appreciate any information they could give,
thanks

Jeff Gundy