Here is an updated summary of where I'm at:

THE SYMPTOMS: At low speeds, off throttle or while braking, like bumper to bumper or parking lot, the engine will shut off with no warning. No stumble, no jerking, no hesitation. Car settings like the clock maintain. The car restarts perfectly every time. I've noticed that around 20mph off throttle the rpms will bounce just a touch like between 800-1000 range it bumps around a little bit. Idles perfect around 600, never shuts down when idling. Drives at high speed like the ultimate driving machine, never turns off at high speed.

MY ATTEMPTS TO FIX (in order mostly)
New fuel pump and filter (tried 2 fuel pumps actually bc I did needed a new one earlier this year).
Replaced both camshaft sensors (not OEM), mechanic did it while I was ill for a short time
Mechanic said he did a vac test
Replaced crank sensor twice, 2nd time was BMW OEM new part from FCP Euro
Oil changed
Swapped and cleaned the MAF
Replaced Idle Air Control Valve (URO), after cleaning the original which was shot and now thrown out
Checked battery terminals and alternator, all looked good
Replaced all spark plugs

What are you using for a scan tool?? We've had lots of people caught by not getting all the codes.

Guys, again I'm sorry for the dual threads and even I'm getting mixed up. Xoutpost is annoying on my phone. Please stick with me. I'm going to solve this and I want to learn more.

I have a simple actron OBD2 scanner. Used over the years for clearing codes and that's about it. I also have the airbag reset tool.

I've now ordered the Foxwell BMW NT510 Elite and also the Veepeek module and have the OBDFision App. I don't know much about them right now.

I also do have a smoke machine and smoke tester. Used in the past when my CCV had a huge wide open gap at the tube down low by the dipstick. I had codes then and sometimes the car would shake wildly, like a washing machine. Funny stories about that around 160k. I tried to smoke test the other day blowing into the resonater tube just after the MAF, I had a lot of pressure to the point where my rubber glove mod, popped off and all the smoke came out. That made me thing my smoke wasn't getting past the IACV or the throttle plate, which I presume was closed. I'll try and resolve from a CCV tube, but any other tips or links on proper smoke testing?

Thanks. Cold weather here so not doing much this weekend

Let's be honest. I'm a hack. It's incredible I've been able to run this car 234k miles with only bringing it to the shop for suspension work AFTER swapping a CV boot myself (just the boot, not even the half axle) and for tires. Also used mechanic for motor mounts and both front and rear control arms. That's it. 23 years. Never once left me stranded.

Anyway - I'm learning a ton watching videos in preparation for my new scan tools. Feel like I'm learning quite a bit about a real approach to diagnostics and will be happy to out this to use.

https://youtu.be/4iIxAI3XQIk?si=sBSLLGIkRDb7WQby
https://youtu.be/pIJdCZgEiys?si=yO_ECALzvmY9XLxG
https://youtu.be/TyYKe4vGl0g?si=dx65KTxE9n3IyWnZ

You ain’t no hack. You’re using your brain trying to figure stuff out. And if you don’t know it you seek it. That’s all that matters.

EDIT: at one point in time I did a DISA rebuild on my M54. All I know is that’s related to air intake control. Not sure if it could be stiff or something and cause issues like this. The scan tool will be the best thing first.

Thanks man. I'm going to check the DISA next time I take things apart. I have a spart DISA and the other one from my 2006. I'm going to clean the throttle body too. Never did that.

Cold winter day here in NJ. Thinking some more. Watching the videos...

When I changed the plugs, the old plugs definitely showed signs of a lean condition, but they were also old yet working fine. Since the stall only happens when decelerating which creates a lean condition on purpose, I started thinking about my Vanos solenoid. I didn't pay much attention to it, but I did notice there is a small oil leak at the banjo bolt or hose, and also my Vanos solenoid is original. I also don't change the oil too frequently since I'm always adding oil... Bottom line, bought a new solenoid and will install before replacing the cam sensors. I googled it, and it says the gummed up Vanos could mimic a lean condition due to its impact on timing.

Anyone have thoughts about this? Otherwise, I'm thinking there must be a vac leak or it's the cam sensors. The videos I'm watching really make sense and pushing me to think logically. If this was a short circuit, it wouldn't only happen at low speed, etc etc

Thanks all.

The Vanos solenoid on the M54 is just the electrical pilot valve, the main spool is in behind it so not like the others where it's all in one. I have trouble with the spool sticking on the wifes X3 (that sets the CEL) but the solenoids are unlikely to cause problems like you are having especially if they aren't setting codes. The solenoids can leak oil and it's not uncommon for the oil line to leak but that won't cause the stalling.

Ah, I see what you mean. The actually plunger part is not part of the solenoid. I now see it's a different part # 11367560298. Can I replace that part and the spring once the solenoid is off, or do I need to remove the entire front cover with the gasket to change it.

You can change the spool and spring once the solenoid is off but I seriously doubt that's your problem. Get your scan tool reading all the BMW specific codes before you further.