There would be no code since the ECU thinks its doing what its supposed to.
I read a lot about this before I got mine. It is programed that way, And Honda will do nothing under warrantee.
There are even units designed to fool it into thinking its seeing a different air temp than what it actually is.
But I guess they don't always work.
Its the air temp to fuel ratio thats causing the stumble.
The ECU is cutting the fuel mixture down before its warmed up enough.
They have this all figured out when you get the reflash done.
Getting my reflash done this fall.