HELPLZ! My B20B integra engine cuts off 3rd gear.

Here's the get down. First time I have taken out
and put in a enginge. I bought my 90 integra with a
blown engine. I bought a B20B from jdm motor's
and installed it into my 90 integra keeping original
clutch, altinater, tranny and PGM intake manifold.
Car started right up and I drove it for about a week
back and fourth to work then my problems started.
First it would idle high and low rapidly then in third
gear pick up a little speed the engine would
straight cut dead then I come to a rolling stop. I
already replaced IAC valve and that wasn't the
proble. Help please with good advice thanks.