S40 Uneven Engine Jerking

Rough idle and jerking? Sounds familiar. I had a similar problem with my S40, though it could be a bunch of things. Have you checked for any exhaust leaks? A small crack can cause mayhem with the engine management system. Also, when was the timing belt last changed?

I haven't checked for exhaust leaks myself. I suspected the oxygen sensor because of the error code. The timing belt was replaced about 60,000 km ago. If it's an exhaust leak, where is it most likely to occur?

Well, the O2 sensor could still be faulty, but exhaust leaks are common on these cars, especially around the flex pipe or manifold gasket. Honestly, without getting under the car and poking around, it's hard to say exactly where. Given the symptoms, and unless you're comfortable with DIY repairs, I'd suggest taking it to a workshop to get it properly diagnosed. Could save you time and money in the long run.

Thank you for the information. I took the car to a workshop, and it turned out to be a leak in the exhaust system, as you suggested. The repair cost was 265€, which included welding the leak. The engine is now running smoothly again.