I have been trying to diagnose a rough idle/misfire condition. I have been using one of these things: http://www.simpson260.com/others/gre...t-11_gt-15.htm
to show me when the spark occurs in the plug wire. There are many other brands that do the same thing and can be bought at any hardware, home repair, dept store. Some just flash a LED and others flash and chirp. I use it at night so I can easily see the flash.
Even when my engine appears to be idling smooth and I hear a steady pulse out the exhaust pipe there is NOT a steady consistant firing of the coil.

 

I'm not sure that tool is suffient to check your spark.
It's made for house wiring and probably isn't fast enough to detect every spark pulse.

 

I would say just pull the plug and check the gap. Could be easily fould that way found 2 of mine clogged up with oil from having a plenum gasket leak.

 

I pulled all the plugs recently and they look like new ones and they have at least 20k miles.
However, I did not check the gaps.
Thanks defiant.