I recently purchased a 2001 Thunderbird, 9500 miles, beautiful shape. It has been running rough between 2000 and 4000 RPMs, took it in to the shop and he found one of the coil wires loose, put in new plugs. Worked fine for about 50 miles, now running rough again, not quite as bad as before. Considering replacing the 3 coils with Nology coils, rather than just replacing one bad one.