380SE sounds like missing on 1 cyl - how to test?

[donbryce]

The problem appeared about a week ago, when it idled great until a restart outside the mall. Ever since it's developed a loping, rough idle, shaking the car when it is sitting idling. It seems to smooth out when in gear and driving normally, but to me it still feels rough.
I read up on what to look for and have a pair of motor mounts on order, but no real gut feel that they are the problem either. What I'd like to try is pulling the plug wires one by one to try and isolate which cylinder may be missing. But I'm afraid of electrical shock from the motor running while I do this, and the plug wires are really hard to get off the plugs.
How would it work if I shut it down and removed the wire ends, one by one, from the distributor instead of the plug, then start it up to check the effect?