Crown Exhaust Treatment Malfunction

Toyota Crown, interesting. Sounds familiar. Have you checked the lambda sensors, NOx sensors, or the catalytic converter? What codes are showing up? Any changes in fuel consumption?

I haven't checked the diagnostic codes yet. Could a defective lambda sensor cause all those symptoms? Is there a way to know if the sensor is the problem, or are more diagnostics needed?

Defective lambda causing multiple symptoms? Absolutely, it impacts the air/fuel mixture. Can you diagnose it at home? That depends. With the exhaust leak, smell, and rough running, it's beyond a simple sensor swap. Take it to a workshop for diagnostics to pinpoint the cause. But yes, lambda failure is possible.

A workshop visit confirmed a defective lambda sensor. The repair was 375€. The car is now running well. Thanks for the help.