I have a 1989 240sx hatchback, auto with 114k miles. Lately the car has had bad problems with the idle, going up and down when stopped, either in gear or out. Sometimes it does a little better if i put it in neutral when i'm stopped, but thats only sometimes. I got the spark plugs, wires, distributor and rotor changed not too long ago when i took it in for a tune-up, and it still does it. Sometimes, when it gets down below 500 rpms, blackish smnoke comes from the exhaust. Along with that, a few weeks ago it decided to start sputtering while driving, but ONLY between 3k and 4k rpms. This went on every day for like i said, a few weeks. But the other day, i went back out after i got home from work, and it was gone, no sputtering at all. But when this stopped, the idle problem seemed to get worse. I have no clue what this problem is because i'm not mr. car guy. If this is a big problem, why would it just dissapear? i was planning on taking it in to the dealer so they could check it out, but since its not doing it anymore, it might be a little difficult to find out, ya know. Does anyone else have any clues that might help me out? thanksin advance
bryan