?? on checking ignition coil

happy new year,i have a 93 escort w/1.9 ltr.I'am trying to diagnose a intermidant roug idle i have changed iac,vacum lines,complete tune-up there is NO egr valve on this one.fuel pump is ok (42 psi).no manifold leak as far as i can see sprayed the entire area no change in idle.i was checking the ignition coil according to the chilton book & they say "with the edis diagnostic cable negative battery lead connected,disengage the positive lead".what do they mean by this i only see one 3 wire plug going to the coil & the edis is wired directly into the fuse box.all i did was chk the ohms between the 2 without this diagnostic cable touched & it read .003 ohms when they say it should be 0.4 or greater any help will be appreciated or ideas of what the problem is thanks

I think a bad coil will normally just quit. Especially when it gets hot. I had the same symptoms on my '93. I replaced the PCV valve and the Oxygen sensor and the problem was solved. Since I replaced them both at the same time I don't know which was responsible. It was intermittent. Engine would almost die but not quite. Has never done it again. My Oxygen sensor was the original with 250,000 miles on it so I guess it was about time!

Mine did the same thing, it turned out to be the idle bypass valve(on top of the throtle body) A quick way th check the coil pack is to pull one wire at a time while running, each coil should throw a spark at least 1 in. to the wire, if one doesn't and the wire and plug is good on that cyl. replace the coil pack. I've had 2 coils fail , both failed on only 1 cyl.

I'm thinking it's not a coil because it only does it at idle....