Let's fix this thing. I'm back 2003 X5 3.0
 

Quick recap. Car is stalling off throttle while decelerating. No warning. No codes. Starts right back up. Brought it to a shop and they didn't do jack shit. No codes, drove it. Scratched their head and gave back to me. Here is a video of the main symptom. On occasion like once every 100 miles it just shuts off, think like bumper to bumper traffic. Not good. I've done and replaced a lot of stuff. So I need to be more pinpoint. Still seems to me like an idle Air control valve issue. When I'm off throttle and decelerating the rpm bounce when it gets to 900-1000rpm.

I'd be okay to buy a Bosch one for $120 but I also don't know where and where to trust. I feel like eBay is shady. Also eBay has the OEM bmw part for like $150 but also shady AF.

https://www.reddit.com/r/BmwTech/s/NxJXnAntZL

Weathers warm I'm ready to dig it. Car has good vacuum at the oil fill cap. Plugs are new, fuel pump is good, fuel filter is new, car runs great at higher speed and idles no issue. Doesn't miss a beat. It's really in the transition from throttle to idle where it's dying. There no jerking when it stalls. Ruling out torque converter. It just turns off and starts up again after I stop and put in park. Both cam sensors and crank are new. Maf is good. I've swapped around coil packs.

I don't know much about the gasoline I6 (and what I DO know, I've learnt here!) but on your Reddit post you mentioned fuel trims are off (presumably +) so that kinda points to a big vacuum leak somewhere? Or more than one? :dunno:

*edit* oh, I forgot to ask... is this only happening when braking (to slow down) or does it also happen if you simply take your foot off the gas pedal? If it only happens when braking, your brake booster might be your vacuum leak. ;)

I don't see any signs of a vacuum leak. Shop didn't even bother to do the test and brushed it off after asking multiple times. I have suction at the oil fill cap. Nothing crazy, just right. I spoke tested it and didn't see anything. Fuel mileage is okay, so maybe it's a small leak somewhere near the Idle Air Control Valve.

see my edit on my previous post re. brake booster... ;)

Yeah, no symptoms on brake. The video is just foot off throttle, limited or no braking since I was on my back street. The rpm bobble became more noticable after I replace the original iacv with a cheaper new one. I used the URO brand that fcp sells. Find it hard to believe its shit right out the box but that's what I'm leaning toward. Just hate to spend $500 on one only to see it isn't the cause of my issue

All the non OE parts are just "adding to the soup" like Clavurion says ;) If the aftermarket IAC motor made things worse then it would be a good idea to replace it with a new OE one, maybe part of the problem, maybe not the problem at all but a reasonable thing to try. And yes check for vacuum leaks and "passing" a smoke test doesn't mean there is no leak. If you posted this multiple times on multiple forums with different information it's adding to the soup as well.
Are you using a diagnostic platform that is going to get all the codes ??

Remove old IAC and shake it. If it doesn't rattle, it's stuck or gooey. Blast it through the airway with brake or MAF cleaner while shaking it. This fixed a long-standing fuel trim/O2 sensor code (M54) that popped up weekly.

If it has truly failed, pop for the OE part. The $25 Chinesium parts on the hamazon are junk.

Do you have any way of measuring fuel trims while driving with a warm engine?

Long term fuel trims above +5% would tell you if you have a vac leak..

I use the OBDFUSION phone app in conjunction with an OBD2 WiFi reader

Also, the idle speed control valve rarely fails altogether.. it does stick and require cleaning now and then… A used Genuine BMW ISCV is likely better than a new aftermarket part.

I ordered a used OEM valve. I don't trust the new part sellers. Lots of knockoffs on the bosch. Really hoping this or throttle body gasket fixes this.

Fuel trims point to a vacuum leak. Did you check the intake elbow? You might need to smoke it to find it.
Wow, lots of miles on it.
Please post O2 fuel trim levels. Short term and long term.

Dang, too from me to smoke. I have a nice little smoke machine.