jfoj, you're on duty early this morning!
OP, the bouncing idle you had been having sounds like it could be icv, of course, and that would cause your stalling. Did cleaning the icv have any effect?
Have you checked the vac lines behind the intake manifold? I know you said you replaced all hoses, but wonder about those?
Anyway, I really do think you need to get codes read. If it's none of the usual suspects, then I'd think codes might point to some sensor or the like.
Have you done any 'non-stock' things to your car you didn't mention? After your engine swap, was your car running good, or did the bouncing idle happen right away?
Upcoming comedy shows: May 20, Greenwich Village Comedy Club. 6 p.m. See Facebook for other shows and PM me if you can make one...love to see you there!
A recent set: https://youtu.be/995gLmVEVZk
Mangofy your E46!