Will a bad flex fuel sensor cause the engine to shut off. Not stall out… it just stops running.
No. The flex fuel sensor or called the fuel discriminator only tells the computer when to make adjustments to engine timing and injector pulse widths depending on the concentration of ethanol in the gasoline. So if there were a problem with this sensor the engine would still run but poorly.
You describe is more of an input problem to the computer. Something like a faulty crankshaft position sensor as one example.