As 67dart273 you can acurately measure resistance in the single digit range with a two wire multi-meter. Low resistance measurements can only be accurately measured with a 4 wire meter.
That being said the fact that it happens after the car has been run for awhile would suggest you have a temperature induced break down inside the coil (if it's not something un related). You will likely not be able to check for this with a multi-meter since it is happening at temperature and high voltage.
Best thing to do is borrow a coil from someone and try it. If the issue goes away then you know its the coil.
