leading coil?
 

How do you know if the leading coils are bad?

I read somewhere here an easy way to check the coil while its on the car is to unplug the connector to the coil OR remove the two spark plug cables from the TRAILING side and see if your car still runs. It should start and run but very rough. (this is to check the leading coils while still on the car)

Vice versa for trailing coils.

If its already off the car, you can check the resistance on the primary and secondary sides with a multimeter. I forget exactly what the resistance should be, but its in your haynes manual. If you dont have one, someone here can tell you what those values should be.

Hope this helps
TRU

Yep. Just backing up TRURX7. Pull the two upper trail plugs off and put them where their spark will do no harm . Start the car. The car should run just as if everything was connected. Trails are just for emissions clean up and you'll never know they're disconnected. But if the car runs rough or erratic......you've got some type of problem whether the lead coil, plugs, wires or timing.

Just a bit more info on the leading coil to help your diagnosis. It's a single double post coil, not two seperate coils. If it stops working, neither leading plugs will fire, so you won't get that running-on-one-rotor sound/vibration. It'll run as smooth as normal but with dramatically reduced power.
BTW, before blaming the coil make sure the plugs and leads are good. They more likely to fail than the coil. :)

Best bet is with the car is running, just disconnect the electrical connection at the coil. This way there is no "hard" starting with 2 wires disconnected, and you don't have the possiblility of a shock from 1 of the wires if it's dangling around...Have done it many times. You can do this with either coil.
Hope this helps.