Stalled and terrible driving performance

More info to come here on my 1993 VW Eurovan that stalled and had terrible performance recently. Initial assessment indicates that a completely dead auxiliary battery could have been creating a strain on the electrical. I will be performing some test drives and further testing. After disconnecting the auxiliary battery and charging the main, the EV was able to start immediately. I need to take a short test drive (with a bike inside just in case).

UPDATE: Since the aux battery was disconnected, the EV has been running and starting better… and stayed running. But when I replaced the O2 sensor, performance also improved. At this point, I may still have a vacuum leak, exhaust manifold crack (I know it exists, but haven’t see or resolved), and might just need timing/tune up.