If the exhaust broke just in front of the cat, that would explain a lot! The O2 sensors are expecting exhaust and getting air instead. Their readings are way off, the sensors not getting hot enought to keep clean, and the Lambda light turns on.

Take the exhaust pipe and CAT off and bring them to a welding shop. That will fix most of the problems. Check the exhaust hangers and make sure they still support the pipe, if they rust off that will cause the crack.

The plugs will foul from the ECU being told to enrich the gas/air mix by the O2 sensors. I suspect the plugs are completely black and the rings washed with gasoline again.

Klaus
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Praying for Cynthia Amendt, heaven bound