Mercedes GLS rough idle and acceleration issue

Your situation with the Mercedes GLS does sound concerning. Uneven engine running can indeed stem from an exhaust leak, but other factors can contribute. I encountered a similar problem with my old Volvo V70. The symptoms were near identical: rough idle and hesitation upon acceleration, accompanied by the check engine light. In my case, the issue wasn't solely a leak, but a combination of a small exhaust leak exacerbating a failing oxygen sensor. The engine control unit was receiving faulty data, which in turn affected fuel mixture and timing. Have you had the error code read? Knowing the specific code can greatly narrow down the possibilities. Also, inspect the exhaust system for any obvious signs of damage or corrosion. It might be a small crack or a loose connection. While fuel injectors, crankshaft sensor, and timing belt issues can cause similar symptoms, they usually present with distinct error codes.

The error code indicated a 'system too lean' condition. Does this align with your experience and the potential exhaust leak/oxygen sensor issue? Where exactly did you find the leak on your Volvo? Was it easily visible, or did you need special equipment to locate it?

A 'system too lean' code certainly supports the possibility of an exhaust leak before the oxygen sensor, as it's introducing unmetered air into the system. Think of it like this: the engine is trying to breathe, but it's also sucking in extra air through a crack in the pipe, throwing off the air-fuel ratio. In my Volvo's case, the leak was located near the catalytic converter. It wasn't immediately visible; I discovered it using a smoke test. A mechanic introduced smoke into the exhaust system, and we watched for where it escaped. Given the complexity of modern vehicles, and the potential for misdiagnosis, I would strongly recommend a visit to a trusted workshop. They'll have the proper equipment and expertise to pinpoint the exact location of the leak and assess the functionality of your oxygen sensors and other components. It is also important to exclude issues with fuel pressure which can be caused by faulty fuel injectors.

I took it to a workshop, and they performed a smoke test, just like you suggested. Turns out there was a small crack in the exhaust manifold. They repaired it, and the total cost was 265€. The engine is now running smoothly. The 'system too lean' error is gone. I really appreciate your help!