I hope I am not being premature here but I think I have the idle issue solved? on my 91 Regina non turbo 740. Last year 2022 I put on a whopping 125 miles on this car only because it had issues with not starting like it use to. When it did start the runnning was terrible with backfiring stuttering and so forth. All this was solved by removing the accumulator/pulsation dampener...call it what you want...on the fuel sending unit. There is only one intank fuel pump on the Regina cars and this device was on the output side of the fuel pump. Since the fix I have been having idle issues. There were a few false positives but just recently I believe ( fingers crossed) I nailed the fix. After triple checking all vacuum and electrical connections the rpms would momentarily bog down every time I selected a gear or even turning on the ac, essentially when the engine was loaded. As a last resort , my patience running thin , I decided to swap out the ECU again along with a new MAP sensor. I was now reinstalling the original ECU , the one I deemed bad before , but before I did I cleaned the terminals with electrical contact cleaner. Now I am not sure if that did the trick or maybe readjusting the TPS and TB tolerances or just luck on my part. The engine since then is performing like a charm with no rough idle , no difficult starts.
At this juncture might I say thanks to all for your suggestions. Next task is to install a new mid muffler as the present one is ratlling like crazy and even has a few holes in its pipes.
Regards
Paul