The fuel economy on the van hasn't been great for a while, and Stephan suggested that it could be the oxygen sensor. He was on about taking it out and testing it, but I figured I'd just put a new one in there and see if that solves it. The new one arrived today, so I swapped it in. Now I just need to drive somewhere to make sure it works OK, and fill up so I can test the fuel economy. Here's hoping that problem's solved.