Rough idle until engine is up to temp - Ambient air temp doesn't matter

[ChristopherL]

Hello Group,

I just completed swapping a new (used) M44 engine into my '98 318i.
Seems this is the best place to go for M44 questions.

The car has a "lumpy" idle and "stumbles" coming off idle when the engine is cold. As soon as the engine is up to full temperature, the idle is perfect and it accelerates/revs perfectly. Before the car gets to full temp, it bogs/hesitates/stumbles when accelerating or reving while standing still.

This issue is present regardless of ambient air temp. For example it was there today with 70* ambient air temps.

I have not yet tried to pull any fault codes, but there is no Check Engine light on.

It appeared all the other rough idle topics pertained specifically to when the air temps were much colder.

Has anyone run into this issue before?

Thanks,
Chris