Audi Diesel Shudders: Common Fixes for Rough Running

I had a very similar issue with my 2010 Audi A4 diesel about 6 months ago. Having some experience with diesel engines, I initially thought it might be related to the fuel system, but it turned out to be an exhaust leak near the manifold. The symptoms were nearly identical, rough idle, jerking during acceleration, and the engine management light. The exhaust leak was causing incorrect readings from the oxygen sensors, which then affected the engine performance. I took it to an independent workshop where they did a thorough inspection and smoke test to locate the leak. The total repair came to 265 Euro, which included replacing the damaged section and gaskets. Before jumping to conclusions about your A6, it would be helpful to know: What error codes specifically came up in the diagnostic scan? Do you notice any unusual exhaust sounds or smoke? Has there been any recent maintenance done on the exhaust system? Does the rough idle get worse when the engine warms up? The air filter and crankshaft sensor can sometimes cause similar symptoms, but based on what you describe, I suspect its exhaust-related. These problems often start small but can worsen quickly and affect other components if left unchecked.

Last service completed at 65000 KM, currently at 69231 KM. The oxygen sensors were recently replaced during the service interval, but the rough idle persists. My diagnostic tool shows P0171 code which points to a lean fuel mixture. The engine management light stays on continuously rather than flashing. The jerking during acceleration seems worse in cold weather, and the rough idle is most noticeable after the engine warms up. I can also confirm there is no visible smoke from the exhaust, but there is a slight rattling noise from the front of the engine. Given the timing belt was done at 60000 KM, I doubt that is related. The spark plugs might need checking though, as they were not changed during the last service. Could a faulty crankshaft sensor cause these specific symptoms?

Thanks for providing those additional details about your A6. While my A4 showed similar symptoms, yours has some distinct characteristics that point in a different direction from my exhaust leak issue. The P0171 code combined with the lean mixture reading and the rattling from the front strongly suggests either a vacuum leak or fuel delivery problem. The crankshaft sensor could cause similar symptoms, but typically produces different error codes and more unusual engine misfires rather than a consistent lean condition. In my experience working on these engines, I would focus on: 1. Checking the fuel pump pressure, a failing pump can cause lean conditions 2. Testing the ignition coils and spark plugs since they were not changed at the last service 3. Inspecting vacuum lines for any cracks or disconnections The cold weather sensitivity you mentioned mirrors what I experienced before replacing my spark plugs and ignition coils. These components often show more obvious symptoms in cold conditions. Given your mileage and service history, I would start with a spark plug replacement since its the least expensive option. My repair ended up costing about 180 Euro for parts and labor, and resolved similar cold-weather performance issues. Would you be able to check if the rattling noise changes with engine speed? This detail could help narrow down whether its fuel system or ignition related.

The cold weather correlation seems significant, I'm noticing the same pattern you mentioned about spark plugs showing more issues in low temperatures. The rattling noise definitely changes with engine RPM, becoming more pronounced during acceleration. Based on your feedback and comparing symptoms, I'm leaning toward the ignition coils and spark plugs being the culprit. The continuous check engine light rather than flashing also aligns more with this theory than a serious fuel system problem. I'll start with replacing the spark plugs and ignition coils since they're due for replacement anyway. Found a set of OEM parts for about 220 Euro total. If the rough idle and jerking persist after that, I'll move on to checking the fuel injectors and fuel pressure as you suggested. Really appreciate the detailed comparison with your repair experience, it helped rule out some more expensive potential issues like the fuel pump. Will update once I've had the work done.