VW Phaeton Cold Start Fix: Diesel Injector Troubles

Had a similar issue with my 2005 VW Touareg diesel a couple years ago. Having some experience with diesel engines, the symptoms you describe match exactly what I encountered, rough idle during cold starts and inconsistent starting. Initially thought cleaning the injectors would solve it, but diagnostic tests at the workshop showed a failed injector causing improper fuel delivery to the engine. The rough idle and starting problems were due to uneven fuel distribution in the fuel rail system. The fix involved: Complete diagnostic scan, Fuel pressure testing, Removing and testing all injectors, Replacing one faulty injector, Reprogramming the injection system Total cost was 515€ and completely resolved the cold start issues and rough idle problems. Before suggesting specific solutions, could you share: Current mileage? Any check engine lights? When was the last fuel system service? Does the problem get worse in cold weather? Any unusual engine sounds during warm-up? This information would help determine if your issue is similar to what I experienced with the injection system.

Just had my 55805km service last month. The engine warning light comes on intermittently during cold starts, usually going off after warm-up. The rough idle and hard starting definitely worsen in cold conditions. There is a distinct knocking sound for about 30 seconds after startup, which gradually smooths out. The engine misfire seems most noticeable when the engine is completely cold, especially after sitting overnight. Based on your experience, it sounds like I might be dealing with a similar fuel injection issue rather than just needing a cleaning service.

Thanks for those details. Your symptoms mirror exactly what I experienced with my Touareg. The intermittent warning light and knocking sound during cold starts were key indicators of the fuel injection problems I dealt with. Since your symptoms worsen in cold conditions and the engine misfires specifically during cold starts, this strongly points to fuel delivery issues in the injection system. In my case, the workshop testing revealed uneven pressure in the fuel rail, causing those exact hard starting problems and rough running until warmup. Based on the mileage you mentioned and my experience, a cleaning service alone probably wont resolve the issue. The knocking sound you describe during the first 30 seconds matches the behavior of my faulty injector before replacement. Recommend getting: Fuel rail pressure testing, Individual injector diagnostic tests, System leak test at cold start The intermittent warning light suggests the ECU is detecting fuel delivery inconsistencies, just as it did in my case. The repair costs should be similar to what I paid (around 515€) if its indeed the same fuel system problem. Given our identical symptoms and the shared vehicle platform, getting the injection system properly diagnosed would be the next logical step rather than attempting simpler fixes first.

Thanks for the detailed explanation. I agree the symptoms point to injection problems. Based on your repair experience and costs, I will schedule diagnostic testing this week to check the fuel rail pressure and injector performance. Makes perfect sense that cleaning alone wont fix my cold start problems since the symptoms are so similar to what you encountered. The way you described the hard starting and knocking sound matches my situation exactly. I will have them focus on testing the fuel delivery system and injectors while the engine is cold, since thats when my issues are most noticeable. Hopefully the fix is straightforward like in your case. The 515€ repair cost seems reasonable if it completely resolves these frustrating cold start issues. Will report back after getting the proper diagnostic tests done. Thanks for sharing your workshop experience, really helped confirm my suspicions about the injection system being the root cause rather than just dirty injectors.