Poor idle with revs dropping and occasional engine stall when coming to a stop. The problem went away for a little while since doing this work but returned some time later. I think it may be linked to a faulty PCV hose (which often splits on these engines) or a bad PCV valve and/or oil separator). Alternatively, another theory is the valves that control the positions of the flaps in the inlet manifold are - this should throw up an error code, but anecdotal evidence suggests the fault code doesn't always occur.