If u suspect a bad coil ohm out the secondary (across the towers) and it should be around 12.7 k ohms iirc. Coils are pretty durable and while that doesn't check the primary i think the secondary is where most problems will show up when a coil is bad. Allot of times it will get worse as it gets warm. The same is true of a ignition module the and that is far mor likely to go then a coil. If you have a problem u may get better feedback by just telling people what is going on.