Where can I find the part number of my '73 1.7 ECU on the ECU? I haven't found any identifying part numbers and want to make sure it is right for the D-Jet system. I couldn't find info in my searches

Originally marked with a Bosch label with part number. Label color and location varies. Often a red or orange label on cover, or a black and white label on the edge.

I see what might have been a label. It appears to be painted over
Any other way to ID a box?

these 3 pages from factory workshop manual might help.

Click to view attachment Click to view attachment Click to view attachment

There is sometimes a white lable inside of the ecu case with the Bosch part number or stamped into the case itself.

The adhesive label on mine had long since travelled to the Autobahn over the Rainbow. I had to open up the metal box and get the number marked on the circuit board.

I did some red rag rubbing this AM and was able to disclose the numbers on the painted label! It is right for my car. Seeing the MPS was sealed and riveted and the ECU is right for the car, I guessing it's pretty original.

I'd still like to try another to see if it affects my incredible lean idle

Here’s what a discovered …Click to view attachment

Have you tried the idle mixture adjustment knob? That ECU should have one.

Yes, I currently have the enrichment knob at full rich. Something has changed recently after 1000's of happy miles. I've been reading, searching, bench testing etc for some time. I'm working with a wide band AF meter. I've got an incredible lean stumble leaving stop signs as well as a wavering lean idle (16-18).

I'll report/ask more once I chip away at all of the "regular" challenges associated with the D-jet system, distributor and all the other things I've read up on for the last 8ish years of ownership. Like @rjames , I have been eliminating things, one by one with the associated frustration of "no luck, yet".

When I do ask for help, I'd like to be prepared for the suggestions and help and questions that come with those "help threads".

I haven't given up, yet!

Unless these have been done recently, put the ECU down until you...

1stly: Install a new fuel filter and check your fuel pressure for spec or irregularities
2ndly: Send your injectors including the CSV out for cleaning/flow testing.
3rdly: Reinstall the cleaned injectors and road test

Avoid making changes/adjustments that may not be needed or appropriate to fix a system that apparently has worked well for years as it was.

All of those items, Jeff have been done…some more than once! I have a long list of checks, adjustments, repairs and test drives that I’ve completed. Again, once I get to a virtual dead end, I’ll ask for more help from those if you that have been there and done that!

I’ve utilized the past collective wisdom of this great forum extensively…but a lot of you have multiple ECU’s and MPS’s for a reason

speaking of...have you tested your MPS?

Yes, for your consideration, I rechecked my MPS per PB Anders' stuff. Both resistance numbers are as specified and his vacuum test, pull 10" of mercury and if it drops to 5" within a minute, it's a leaker. Mine drops 2.5" in one minute. According to PB, that's good enough.

Whether or not that's good enough is a big grey area to me. The only other MPS I have access to, sealed and never opened, leaks to 5" within 20 seconds!