Lexus SC exhaust leak

That sounds familiar. I had similar symptoms on my old Saab 9-3 – check engine light, sluggish performance. Did you happen to notice any hissing sounds coming from under the car, especially when it's cold? I eventually found a small crack in the exhaust manifold. Could that be it?

Thanks. I haven't checked for hissing sounds. Could a small leak cause such big effects on engine performance and fuel efficiency?

Absolutely! Even a tiny exhaust leak before the catalytic converter can mess up the oxygen and temperature sensor readings. The ECU tries to compensate, leading to problems. Checking yourself depends on how comfortable you are under your car. If not, take it to a workshop for a smoke test. They'll find any leaks fast. Hope this helps!

I had the car inspected at a workshop based on your suggestion. There was a small leak in the exhaust system affecting the exhaust temperature sensor readings. The total repair was 265€, including the sensor replacement. Thanks for pointing me in the right direction.