[Elwood]

Finally got some time Sunday to investigate further. Rechecked all the electrical and vacuum systems under the hood and pulled the spark plugs out of the right bank and re-gapped #4 and #8 to 0.050” from 0.060”. All the plugs (Bosch Platinum ++ ~1500 miles ago) look new. Started and warmed everything up and still have the low RPM miss on #4 & #8 only. Sprayed a water mist on the distributor cap looking for cracks, spark leak, etc. found none. Confirmed the TPS and ISC were within spec also.
When I bought this car is came with a BIG box of parts that the previous owner purchased prior to his “retirement” to an assisted living center and loss of his driving privilege. Most of the parts I’ve installed so far were among these parts in “brand new” in the box condition and I knew there was an ECM in the box so I bit the bullet and dropped the bottom of the dash and pulled my ECM (per the book). I installed what turned out to be a “used” Cardone ECM after transferring the EPROM and started the car. It was still pretty warm from the previous test. The good news is that after 10 minutes of run time on the replaced ECM the loss of spark was undetectable on all cylinders. The bad news is that upon start the engine was loping erratically and when I cycled the throttle the “SERVICE NOW” light came on and the engine idle speed locked at 1400-1500 RPM. The interrogating for error codes indicated a code “100” with all mode lights on the climate control lighted. I shut it down after 10 minutes with no change in this condition and swapped the “old” ECM back into the car. The previous symptoms returned and persist as I commute this week. Both my ECM’s are the cheap Cardone models and do not have the GM part number on them. I’m inclined to go the wrecking yard and finding anther ECM just to see how it behaves but this car can use two different part numbers. Does anyone know how to determine which would be correct? The options are 1226028 or 1226930. My VIN is 1G6EL5788FE647265.
As always, any help is certainly appreciated.