2009 H1 Hyundai 2.5 crdi turbo fluctuations

Sharing an experience.
Had a H1 turbo diesel towed to me blowing steam from radiator.
Step One.
was replace the cylinder head. Ok done.
Started engine and found there was no power.
Step Two.
Found broken turbo and replaced.
Ok done.
The turbo would pulse, surge at low rpm driving.
Step Three.
Check all codes but nothing.
Tested EGR and found over active shutting on and off.
If I disconnect EGR it drives great.
If I restrict intake air the EGR shuts.
If I disconnect map sensor EGR shuts.
Hyundai had no idea of fault and have never seen turbo pulsing like this one.
To end this story after many hours of electrical tests I started engine and run a water hose over oxy sensor for 10 mins.
Test drove the car and it was perfect purring like a kitten.

Ok the question:
Did the ecu hold memory of the cooked engine even after battery disconnected for 2 days and codes cleared?
Did cooling the oxy sensor reset new parameters for the ecu?

I’m just glad it’s finished and out of my hair.