 I'm, like I say, I don't know what to do now other than bring it to a dealer. Well, it could be starving for fuel and running lean, and then that's making the exhaust... Or the converter could be plugged up, which is unlikely on a caravan, but if it was, it would give you a map sensor code, and it would run poorly because it would have back pressure that shouldn't be there. But you could take it to any independent shop, and they should be able to diagnose this and figure out what's going on. The fact that it's running poorly now...