Mark Drillock has warned us on many occasions that the O2 sensor brown ground wire that attaches to engine case near the distributor can have a flakey connection. When I had my engine out for head replacement (and BTW, engine was re-installed in van last weekend and is running well) I checked this wire and found that a PO had crimped on a replacement ring terminal. The connection was very poor, in fact just a little tug pulled the wire from the terminal. The wire itself was slightly corroded so I cut back a ways to find shiny metal and crimped on a ring terminal that had an integral heat shrink covering.

Thanks again to Mark for highlighting this issue.

alistair