Long story so bear with me, I think we might be able to (hopefully) bring this to a near close.
Since this only happens after I begin to stop, or while stopped, I wanted to be sure the brake booster doesn't have a ruptured diaphragm....as this stalling points to either a TB issue or a vacuum leak as we have mentioned.
I checked the booster last night and all was good.
The back story of my fuel pump sealing issue I believe plays a part, I still get random P0440 evap codes as I have been off and on for a year or so, shows it's face a couple times a year. I didn't discover this until about 4 months ago when I replaced my fuel pump.
Right now, I don't have a code when it stalls, but it will show up then go away, I've replaced the gas cap also but still get the codes.
When it began stalling, I noticed misfires then a faulty coil, also considered my new driver using the "cheapest gas" and thought maybe the tank was filled with E85, so my thoughts were elsewhere.
So after I checked the brake booster, I remembered back in June, when my son and I were checking the evap system for leaks. All lines were good, but it was the evap test that perked my interest.
So here's where it gets interesting...
I played around with the Tech 2 on this screen....
The highlighted line for the vent solenoid, you can toggle ON/OFF to close or open the vent in the rear of the tank.
Then go down one line to the purge solenoid command and start changing the duty cycle in 10% increments. You can manually increase or decrease the vacuum placed on the fuel tank and observe the fuel tank pressure sensor data.
The PCM performs a test to ensure the system is "sealed" to the vehicle standards and I believe it has to maintain 12 or 13 mmHg, it won't be the full value of the total engine vacuum as the gas cap has to vent a little. The PCM will also only perform this test with the fuel tank between 15 & 85% filled.
So the EVAP line from the TB, goes into the solenoid, then the charcoal canister, then the tank, then the vent valve.
When the PCM runs the test, the solenoid allows a small amount of vacuum per each 10% step of duty cycle...should reach the target tank vacuum around 30-50% duty cycle I assume, then release.
We. ran it to 80-100% to check for leaks, only heard a slight vent from the gas cap but came up about .2-.5 mmHg short of the mark at times, not all the time.
Instead of backing down the duty cycle of the solenoid, I hit EXIT and the motor stalled....I thought nothing of it as the next time I backed it down slowly and it didn't stall.
I believe since June, the fuel pump locking tabs have not been sealing as well despite the fuel-resistant sealant and now the random EVAP tests by the PCM are commanding a higher duty cycle to reach the target tank pressure, thus ultimately not reaching that target then opening the vent valve to end the test, resulting in a huge void of vacuum that the motor can't keep up with....thus stalling.
That was my thought process, so I pulled the EVAP line from the TB, then capped of the port on the TB.
I have since put 80 miles on it, multiple stop and go sessions.....zero stalling, not even a hiccup.
So it appears that the rusted locking tabs of the fuel pump, have created a leak large enough to keep the EVAP sealing test from reaching it's target gas tank vacuum of 12 or 13 mmHg (not sure) thus resulting in a sudden surge of a lack of vacuum for the engine to overcome.
The likely fix will be a new gas tank.