To underline, maybe someone would have any idea:
I used Autel scanner - it is more useful in this case.

When unplug body module, there is no issues related to communication hang.
when I unplug any of body sub-modules, body module detects it missing.
However, seems ECU somehow also reads some modules, even there only on MPX network. And it still detects unplugged passenger door, which cause hang communication system, regardless door connected or not.
Also, driver door, and tachometer unit, shown during test as having some issues - exclamation mark, but completely readable, until access passenger door.

Any idea where is digging?
Thank you

 

Last weekend I found (via oscilloscope) that there is no communication on TC line, only stable input voltage - 13.8v.
Seems there is short on power somewhere - now it would be wires check again.
Will update once get anything.

 

Update:
on weekend we start the car and it was working about an 1 hour w/o error, however RPM needle was bouncing, and engine slightly change rpms and when needle goes down - slightly "farting" to the exhaust.
I suspect A/F sensor failure (maybe short), or MAF, or something simar that affect on start and cause ECU going into limp mode, this ECU simply might don't have error code for that to show.

For last 4 weekends I worked on BMW with swapped engine, and it failed into limp mode same way as RX300 on startup because detect short on HPFP solenoid, becomes - newer engine with newer sensors and everything else, one out of 3 engine wirings is newer (wirings are not same pinned on ECU side), and old ECU. Once swap to newer ECU, everything on newer wiring begin working, and begin glitches on older wiring side.

That point me to RX issue - it might be something with sensors, especially A/F, it might glitches but still in the range, and since old ECU might not have error for that - ECU get into limp mode. Or it get into limp mode to protect ECU before it "understand" what wrong there.

Any advise what and how to check?

AI advised to unplug A/F, and MAF and see if ECU fail or not into limp mode.

 

@mustkill Please watch this video, Mode 6 will help diagnose A/F sensors. Best of luck!

 

Unfortunately, had not many time to work on it this weekend, so I did quck tests.
Now, when when start engine, the rpm needle is bouncing right away and no error. Engine is almost steady, I can hear only slight quick changes of rpms.
I unplug both AFR and MAF one by one, and nothing changes. Now, when the rpm needle is bouncing - no error. When unplugged - still bouncing.
Originally it was ECU Stable readings (and stable needle), SKID erratic - VSC error. Now both erratic and no error. Make no sense to me, where does it come from?
Also check resistance on AFR - 1ohm only on black wires. I wiggle wirings to see if something changes, and all still the same.