I love to step forward and talk where I have no experience, but I'll just do second best and pass along some information from an aftermarket vendor of engine management electronics. Most everything I've read in their generalized diagnostic tip ring true with my experience for zirconia sensors including the advice I see to use a DMM (on car) to merely confirm an oxygen sensor is seeing stoich crossings and not to judge its performance "... because the numbers jump around so much."

As for the titania sensors, I've never had one in my hand or hooked up to a meter, so I'd love to see a post from someone relating such an adventure with their Regina fuel system.

On page three of this Wells Diagnostic PDF there is a method for testing the titania sensor with an ohmmeter. If you spend some time on their other diagnostic tutorials, you'll find a lot of info on the type of fuel injection of which Regina is an example. They make replacement MAP sensors.