If it's not too late to chip in on this thread, as it seems the problem has been resolved, make sure it is not the cat. I recently had a similar problem with my 01. It was the cat. But to my surprise, the cat was still under warranty (by some special extended warranty) and was replaced at no charge by the dealer. As I later learned, from someone here (Sorry I can't remember who) said that certain Montes, I think the 00 & 01's were covered by this special warranty (10 yr./120k m). My cat plugged at about 9 1/2 yr. 112k m. It went bad just in the nick of time