Further to this continuing saga, after giving the nearly $200 RockAuto distributor additional thought, I took a chance and bought the $75 pick-up coil instead. It took forever to arrive but anyway, I installed it today. Meanwhile, I found two burned wires going from the ICM on the fender well to the ECM (I assume - couldn't really see where it went). It looks like the OEM clip the keeps that harness segment up off the exhaust manifold (this is a 22REC) had left town sometime in the last 30 years and allowed the harness to cook. One wire was burned in two, one was about ready to go and the third was, so far, untouched. So, with all that stuff fixed, off to road test we went. The 10% issue previously mentioned has now gone away also.

Now I'm thinking those two problems have been the issue since fall 2012 when I bought two ICM's. The first one ($75) failed (I thought) 2 days after the 30-day warrantee so I bought an AIRTEX / WELLS with a longer guarantee for $150. The original one was probably OK but how do you know when your customers expect you to plow their driveways and the plow truck won't run?

Again, thanks to everyone who tried to help.

 

I was just searching on net and found a Check Engine Light website.
The check engine light is also known as malfunction indicator lamp (MIL). It shows when having a glitch in the electronic control module of vehicles. Commonly, the check engine light is positioned within the instrument console. In some older vehicles, the check engine light was referred to as "engine" or "trouble", which demonstrated small problems including overheating or flat oil pressure inside the motor. The check engine light is usually of golden or reddish color, and there are two types of it:



http://checkenginecode.com/flashing_check_engine.html

 

Thanks AutoExpert for your input but I don't see the relevance to this thread.