I just bought a 1997 altima and it was running fine for about 1 month. Then it started missing while driving down the road. Now it is stalling at idle. I changed the plug wires and then the plugs. The plug tips were black and chalky. I thing that the timing is off a little. After I changed the plugs it runs fine. But I think that it will start running bad again in about a month of driving with the new plugs. I would like to know if this could be doing this because of the timing and what the timing should be set at. The car has 130000 miles on it.