[ShadeTreeMech]

Originally Posted by Phantom

A bad O2 sensor is most likely to read lean since the resistance will change causing the mV to read lower thinking that it needs more fuel. I do not see how it could become less resistive with age.

From the wikipedia article
Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles (50,000 to 80,000 km). Heated sensor lifetime is typically 100,000 miles (160,000 km). Failure of an unheated sensor is usually caused by the buildup of soot on the ceramic element, which lengthens its response time and may cause total loss of ability to sense oxygen. For heated sensors, normal deposits are burned off during operation and failure occurs due to catalyst depletion. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the fuel economy worsens.

Originally Posted by dennyt

I'd recommend a hand-throttle, or perhaps a sideways gas pedal for the electric system?

Originally Posted by brucey

That's the plan! Except it's going to be much simpler than that:

I'm simply going to have 2 independent throttles. I'll control the electric motor with my hand and the regular gas engine with my foot.

Just my 2 cents worth