Tilly and I took the van to San Francisco to see Mum and Dad. Having picked them up, we went to Ocean Beach, where Tilly got to run and play on the sand and paddle in the sea. We went from there to Fort Funston, where we watched the hang gliders zipping back and forth. After a stop at Starbucks, I dropped the parents back at their hotel and headed home.
Now, on the way there, all freeway, I'd stopped and filled the van and it had got 15.5 mpg, which is where it's been since the "rag incident". I figured that the new oxygen sensor hadn't fixed anything. When I got home, I filled it up again, and driving around San Francisco with its hills and traffic, and then the >100 miles on the freeway home again netted 17.25 mpg. Fixed? Maybe... I think I need some more data points.