Outback Diesel's Cold Start Power Loss & Rough Idle

Had the same symptoms on my 2012 Subaru Forester diesel. The rough idle and power loss turned out to be a combination of issues with the fuel system. Initially thought it was just a clogged fuel filter, but diagnostic tests revealed loose connections at the fuel filter heater plug. When cold starts become difficult and engine stalling occurs, its often tied to the fuel heater assembly. The wiring harness connection to the fuel filter heater can deteriorate over time, causing intermittent power supply issues. This creates problems with fuel warming during cold starts, leading to poor combustion and the symptoms described. The fix required replacing the entire fuel filter heater assembly and rewiring the connection point. While not the most expensive repair, its crucial to address it promptly as continued problems can stress other fuel system components and potentially damage injectors. Would strongly recommend getting it checked soon, as leaving it unattended could lead to more serious engine performance issues. The check engine light and poor fuel economy are classic indicators of fuel delivery problems in these diesel engines.

Thanks for sharing your experience with the Forester. Its good to know the fuel filter heater was the root cause. My Outback is now at the shop and they are doing a full diagnostic on the fuel line system. They mentioned similar issues with loose connections and possible need for filter replacement. Curious, do you recall what the repair cost was in your case? Also, have you experienced any fuel efficiency issues or engine stalling problems since getting it fixed?

Thanks for asking about the follow-up. The repair on my Forester was actually quite straightforward, the mechanic found a faulty cable connection at the fuel filter heater, which was causing the power loss and rough idle issues. Total cost came to 95€ for fixing the connection, which was much less than I initially feared. Since the repair, the fuel system has been working perfectly. No more engine stalling or power delivery problems, even during cold starts. Fuel efficiency returned to normal levels immediately after the fix, and the diesel engine runs smoothly now. The key was catching it early before it could cause damage to other components. Your mechanic seems to be on the right track with the diagnostic approach. The symptoms you described match exactly what I experienced before the repair, and loose connections in the fuel filter heater assembly are a known weak point in these engines.

Finally got my Outback back from the shop today. The mechanic found exactly what they suspected, a failing fuel filter heater assembly and some dodgy wiring connections. The fuel line inspection showed the filter was also partially clogged, so they replaced that too. Total bill came to 280€ including parts and labor. More than I hoped for, but still better than risking bigger issues down the line. The diesel engine is running like new now, no more rough idle or power loss problems. Even the cold starts are smooth again, and the check engine light has stayed off. Took it for a good test drive and the difference is night and day. Fuel economy is already showing improvement. Really glad I got this sorted before it could cause any serious damage to the engine. Thanks again for the helpful advice, it definitely made me more confident about what needed fixing.