GLK rough running and jerking

Jerking during acceleration combined with a rough idle and a check engine light could indicate a number of things. You mentioned the error memory – do you happen to know the specific error codes stored? That would be immensely helpful. Ignoring those for a second, have you considered a possible engine misfire? A leak in the exhaust system prior to the oxygen sensors could also cause such symptoms, leading to incorrect fuel trims and a rough running engine. But before jumping to conclusions, could you verify the condition of your spark plugs and ignition coils? Are they original, or have they been replaced recently?

Spark plugs and ignition coils are fairly new, replaced them maybe 20000 km ago. I don't have the exact error codes on hand right now, but what makes you think it could be an exhaust leak? Is it something I can easily check myself?

The symptoms you described, particularly the jerking and rough running, align with potential exhaust leak issues. The engine control unit adjusts fuel trims based on oxygen sensor readings. An exhaust leak introduces unmetered air, leading to inaccurate readings and incorrect fuel adjustments. As for checking it yourself, it can be tricky without proper equipment. Visually inspect the exhaust manifold and pipes for any obvious cracks or holes. You might also hear a hissing sound when the engine is cold. However, a professional smoke test is the most reliable way to pinpoint small leaks. Given the complexity, and without the specific error codes, I would strongly recommend taking your GLK to a qualified workshop for a proper diagnosis. It's better to address this early to prevent further damage.

Thanks a lot for the insight. Turns out it was a leak in the exhaust system, as you suspected. Got it fixed at the shop; cost me 265€. Runs smoothly now.