The American motorist gets blamed for many things, including urban sprawl, global warming, unsafe streets, drunken driving and conspicuous consumption. But it’s not the motorist who makes airbags that don’t work, SUVs that burst into flames, cars that leap violently forward for no reason or engines that spit out their spark plugs. Like air pollution and crowded highways, these problems aren’t new and there’s no sign they’ll end anytime soon.