Dan,
Retracing your problem are we on the same track ?
Appears to overfuel when accelerating.
Or at least you say it does not give “normal” response.
I know you have no problem with the original ECU.
That is a real puzzle.
All the same, hard to think Roger’s slight tweaking of the fuel map causes so much headache.
BTW, did you check the vacuum line to the ECU mentioned by Mike90 ?
If there is a restriction in that line you will not notice in normal cruise or slow throttle changes. But rapid changes while accelerating or starting will delay the information to the ECU and it will not be at the correct point on the fuel map.
Way back you said:
“Testing the throttle pot with the SE-ECU, it runs rich with a minimum idle of 2000rpm, and when I hit the throttle, it still sputters and sounds like fuel is flooding the piston chambers. Heavy sulfur odor from the catalytic converters working overtime.”
You need to be careful when claiming the mixture is too rich.
A weak mixture will not always ignite in the cylinders, but can pop in the hot exhaust.
My experience is not so great I can always tell that failure to fire in the cylinders is due to either too rich or too weak a mixture, especially if it just a momentary thing.
No matter what, you can only get a 2000RPM idle is if you have a lot more air then normal getting into the engine. The throttle pot, ECU, FPR, O2 sensors do not directly account for 2000RPM idle.
A quick answer to the apparent fuelling problem is take the car to a dyno equipped shop. They are common in large towns, and a good operator can quickly zero in on the problem engine performance point and see what gives.
My guess is it will cost about US$100 - US$200 for 30 to 60 minutes on a dyno.
Take both ECUs, then you can try both on the dyno to see the difference.
It is true that with the ECUs you have the only way to make change to the base fuelling map is to change the FPR setting. I doubt that is the answer.