when i had a b series tbody on my car for s short time on a d16y8 intake manifold, because thats the motor i have the y8
it did the same thing when it was right at 1900 rpm it would stutter and shake and breakup and almost die if i didnt give it gas
it was because on that tbody there was no plug for the iacv so it was just left disconnected. i played with the idle screw and got the idle perfect but it still did the problem at 1900. the idle is also strange because a y8 is setup to have a fast idle control for when its cold it will idle high but my b series tbody didnt have one on it.
It also had the cel for the disconneced sensor
the way i fixed all of these problems was to take off the b series tbody. i sent off my factory tbody to maxbore and got it bored out to the same size as a b series tbody and put the stock borred out tbody back on so all the sensors could actually be hooked up correctly and of course it fixed everything. no messed up idle no stalling no breaking up no cel.
i know this honestly dosent help you much, but me and my buddy tried everything and could not fix that problem instead of living with it i took the factory d series tbody that i knew would work the same one your intake manifold wants to accept and is setup for with all the sensors. sent it to maxbore to get it borred out to b series size which you could do if you want to and reinstalled it.