Hi rstski i had this problem when i converted and it turned out to be a air leak from the inlet manifold gasket which caused this.

but saying that my car drives very juddery at low revs and i believe its because i vented the idle control valve pipe aswell and is causing a slight leak.

also disconnect your idle control valve when nice and hot and set your base idle to 750rpm

report back your results when you fit the new cross over pipe.