I have a 1998 Accord LX with 82,000 miles which has been running very well until recently. The car has had the ignition wires, plugs, air cleaner and dist and rotor replaced several months ago. The timing belt and water pump were changed at the dealer two years ago. I have the ac on most of the time in hot weather; the idle fluctuates when the compressor cycles on and off which I understand is normal. However, now I am not using the ac in Fall weather the idle imparts a quick vibration through the steering wheel and the tach still shows my normal 700-750 approx reading. This "roughness" is also felt in the floor when accelerating. It is very subtle but still noticeable to me the driver. I know it is difficult to make any diagnosis from what I have given you but please give it your best shot. I am thinking engine mount??