Well, I did my homework today regarding code P0153, here on AF, and also on the internet. It may have fried my brain a bit (stoichiometric air-fuel ratio anyone?).
It appears, and this is wishful thinking of course, that something as simple as lousy fuel may have been activating this code. My Windstar sat for 'a while' before I bought it in April, and it had maybe 1/4 tank of fuel in it at that time. Also, I've been reading that present day ethanol and methanol additives attract water to the fuel tank. Anyone know about this? And is there a tried and true water eliminating additive anyone could recommend?
The plan, which has been changing quite a bit, is to test the offending sensor if the code comes up again (eight days now, no problems). I'll need to figure out how exactly to 'backprobe' the sensor. Haynes just says 'do it', but hopefully someone here has left some guidelines. I understand that you can fry a sensor by testing it the wrong way.
Thanks for all your help everyone, it's very much appreciated.
Regards,
Michael