Pontiac Repair: GrandAm misfire - started abruptly, trouble shooting guide, ohm meter

Question
-------------------------
Followup To
Question -
1994 GrandAm Quad 4 SOHC 2.3L, has 275000 km, mostly highway driven, running great until recently; now have serious misfire at idle, and won't run right. I recently installed new plugs and O2 sensor. I followed trouble shooting guide... checked injectors, when #3 disconnected, there is no drop in revs - I checked for voltage at injector-OK, and then tried switching injectors 3 & 4, but problem stayed with #3. I installed temporary spark plug leads from the IDI unit, and tested for spark at all plugs-OK, except when #3 plug lead disconnected at idle the engine idle speeds up and smooths out. Putting the plug lead back on makes the engine stumble and slow down. This seems baffling - any idea what is going on?
Answer -
The most probable cause is the coil housing is shorted internally or a bad coil. The coil housing is the plastic part that the "plug wires" are attached to. You can check it with an ohm meter. Leave the coils inside and check for resistance between all 4 terminals. You should get a reading of 5-7 ohms between terminals 1&4 and between 2&3.
If you get any readinds between 1&2 or 2&4 etc., the coil housing is bad. If the readings are higher than 7 ohms then take the coils out and recheck them.

Follow up question - Thanks Harold; I did as you recommended, with coils both in the housing and out. The readings I got are 6000 okms  between both 1&4 and 2&3 so the coils themselves look good, but with the coils in the housing I also got resistances of about 400,000 ohms between 1&2, 1&3, 4&2, and 4&3. Would you say these high resistance readings definitely indicate the coil housing is the problem, or are they within range of "normal" ?

Answer
Yes the housing is bad. You should only get readings between 1&4 and between 2&3 with the coils installed, and no readings with the coils out. You may also want to replace the plug wires (boots) too. The springs inside of them tend to get corroded.
Sounds like your problem is solved, but if you need anything else, feel free to ask.