You may want to have a look at this thread, Captiva is the sister car of the Antara. It seems to point at theexhaust gas recirculation(EGR)
This bit was interesting:
"Looks like the EGR valve on the Captiva is a common problem. The garage has told me they cant get one for over a week. Chevvy says they are supplying around 60 of these a week."