Hi!
I am new to the forum, so welcome everyone.
The problem we have here is most likely gaskets (uper or lower) on the inlet manifold, Parished gaskets on the throttle body, or air leak somwhere. One of the chap from Polish Jag forum had that problem as well and manifold gaskets, cat converter B1 sort the problem out.
I know its an old post, but hopefully will help someone