Hi,

You need to find out how great of condition the your ignition system is in.
Having soot deposited on brand new plugs is not normal unless you have the wrong heat range plugs in there or not a very good spray pattern from the injectors.

As I remember, I think you said the car sat for a long time and the engine is fairly new to the body.
Maybe the octane factor is low if there’s old gasoline churning through the pumps. That would affect the spray patterns.

The next thing to observe is the amount of time it takes for the engine to shut down as the ECU can do this with fairly precise timing in it doesn’t get proper feed back from a few sensors. It can initiate a shutdown for lack of a proper signal like from the CPS.

If you have a timing light put it on there to see if you are losing ignition spark as if the key was turned off and back on. I had a module on my old Ford truck do that while traveling down the road.
I recently had an issue with my 1993 doing something similar after thinking and having a bad in-tank fuel pump. The car would only run for a shot time and die. It wasn’t the pumps shutting off.

I change out the CPS and nothing changed but I caught the ignition dropping off with a timing light.

I then went to the middle man with great suspicion. It’s call the ignition relay module behind the battery.
I then remembered that when I got the car the connector on that item was busted and I had jury rigged a wire tie to hold it to the module since the spring clip was gone.
The Previous Owners mechanics must have buggered it up in the past.

I replace the connector from another harness I acquired later and thought it as a great thing to correct no matter what.
But it did the same thing again. This gremlin would shut down the engine just about precisely 30 seconds after starting during it warming up stage. The ECU is critical about emissions sometimes but I don’t remember getting a code for anything. I assume you do not have an EGR light either?

The ECU has a programed sequence of steps from start to finally warmed up. It looks for perimeters to be so-so, I’m thinking?
Well, I thought why couldn’t the middleman have a fault of just turning off like my old Ford Module?
I decided to change it out.
It has to work precisely in order to provide proper timing to the coil.
Maybe it’s malfunctioning OR the ECU is not good with it doing something some time or another?

Got it replaced and lo and behold the engine just kept on running and running! No more shut downs.
It has run now for at least 1,500 miles without any hiccups!

Well, that is except for the heater/air conditioning fan motor dying on my last trip.
What a job that is to do to the whole dash. I took it out to grease the windshield wiper shafts as one of those started screeching.
This was my second fan job to do out of my six cars. So I have been pretty darn lucky. 😊

I know your issue is definitely easier to fix.
So with this I will leave you with looking very strongly at your ignition system and the fuel quality.

These are definite possibilities of being “in the realm of unknown things” about your car.

Phil