LFA Exhaust Temperature Sensor Issue

Yep, fought a similar gremlin on my old Volvo V70. Exact same symptoms: check engine light, felt like it was dragging an anchor, and the fuel economy tanked. For me, it turned out to be a leak in the exhaust system messing with the sensor readings. Exhaust temperature sensors, or EGTs, are there to monitor the temperature of the exhaust gas flow. Car's computer (ECU) uses those inputs to protect components like the catalytic converter. A leak downstream of the sensor may fool it.

A leak, huh? Where exactly was the leak on your Volvo? And which sensor?

On the Volvo, it was a cracked exhaust manifold. Pain to get to, and the sensor was the one right before the catalytic converter. I'd get it checked out by a shop. They can do a smoke test to find any leaks in the car exhaust and pinpoint whether it’s the sensor itself or something else causing the false reading.

Thanks for the help. Took it to a shop, and you were right. A small leak was detected upstream of the exhaust temperature sensor. Sensor replaced and leak fixed. Total cost: 265€.