No, you don't need a download, unless your car is a standard trans. I don't recall the cost per se, but I think I pay appx $200.00 for one. Used could be problematic, you've got about a 50/50 chance of getting a good one. As far as damage goes, well that depends on whether or not it has failed towards lean or rich. Rich, of course, fills the crank case with fuel, and fouls the plugs, and eventually smuts up the 02 sensors as well. On the lean side it can somewhat melt the catalytic convertor. So, with a rich problem, as long as you change the plugs and oil rather frequently, there shouldn't be any long term damage...but then fuel isn't getting any cheaper. Hope this helps,

Chris