If you're feeling this vibration through the floor/body and not the steering wheel then it's unlikely to be wheel balance. If the car is sluggish at slow speeds you might be feeling 'hesitation' as the engine tries to get enough air and fuel.

Check the easy things first: clean or replace your air filter and replace the fuel filter(s). (you'd be amazed at how many folks neglect to keep a clean air filter in older cars!)

Next, the car is 12 - 13 years old and is probably running on the original wire set. If you haven't done normal "tune-up" maintenance, now might be a good time to replace those fuel and spark related maintenance items. A good, new wire set will deliver a much stronger spark and resist missing due to humidity and moisture. And at least check the condition of the spark plugs. (If you don't know what the spark plug tips 'should' look like, there's a great series of photos in just about every Chilton book ever published).

With the regular maintenance done (which needs to be done anyway) you will rule out a lot of little things AND your car will be in much better shape for the next ten years of driving.

- michael