Subaru Lucra: Rough Idle & Power Loss Points to Bad O2

I had nearly identical issues with my 2007 Subaru Justy last year. Having some experience with fuel system problems, I initially thought it might be the oxygen sensor, but it turned out to be more serious. The symptoms matched exactly, rough running, stalling at idle, and the check engine light was constantly illuminated. The engine would also surge unexpectedly during acceleration, which was concerning. After taking it to my regular workshop, they diagnosed a faulty fuel injector that was causing an overly rich mixture. The diagnostic process involved checking both the throttle body and catalytic converter, but the root cause was definitely the injector. The repair cost came to 515€, including parts and labor. The fix completely resolved the issues, no more stalling, smooth acceleration, and the check engine light cleared up. The whole repair took about 4 hours. Before suggesting more specific advice for your case, could you share: Have you noticed any unusual fuel consumption? Does the problem get worse when the engine is cold or warm? Are you getting any specific error codes from the check engine light? Has there been any recent maintenance done on the fuel system? This information would help determine if your Lucra is facing the same injector issue or if its something else in the fuel delivery system.

Last service was at 19500 KM and Im not getting any specific error codes. Just checked my fuel consumption and its definitely higher than usual, about 20% more than normal. The rough running and stalling are much worse when the engine is cold, especially in the morning. I checked the spark plugs last weekend and they looked pretty black and oily, which probably indicates a rich fuel mixture. The intake manifold also makes a slight whistling noise during acceleration. The check engine light started flashing yesterday during heavy acceleration. Think I should get the fuel injection system checked first before looking at other components?

Based on those additional symptoms, especially the black, oily spark plugs and the higher fuel consumption, this does sound very similar to what my Justy experienced. The cold-start issues and whistling noise actually point to possibly multiple connected problems. The mass airflow sensor often works together with the fuel injection system to maintain proper air-fuel mixture. When I had my Justy fixed, they actually found that while the faulty injector was the main culprit, the mass airflow sensor was also malfunctioning, causing incorrect fuel trim values. The flashing check engine light during acceleration is particularly concerning, as this typically indicates a catalyst-damaging condition. The rich mixture could be damaging your catalytic converter if left unchecked. Suggestion: Get both the fuel injection system and mass airflow sensor checked immediately. The whistling noise could indicate a vacuum leak, which would also contribute to the rough running. In my case, waiting too long led to additional repairs being needed. A diagnostic check should run about 100€, and based on my experience, if its the same issue as my Justy had, you might be looking at 500-800€ for the complete repair depending on which components need replacement. Would recommend asking the shop to specifically: Test fuel pressure, Check all injectors for proper spray pattern, Clean or replace the mass airflow sensor, Inspect oxygen sensor operation, Test for vacuum leaks This should identify the root cause without replacing parts unnecessarily.

Thanks for the detailed response about the diagnostic steps. The black spark plugs and increased fuel consumption definitely match what I noticed. That flashing check engine light during acceleration is especially worrying, I didnt realize it could indicate potential catalytic converter damage. I just scheduled an appointment with a local shop for tomorrow morning. Asked them specifically to check the fuel injection system, mass airflow sensor, and test for vacuum leaks as suggested. The intake manifold whistling noise has actually gotten a bit louder today, so mentioning that to them as well. Really hoping to catch this before it causes more extensive damage. Will post an update once I get the diagnostic results. Based on the repair costs you mentioned, I better be prepared for a 500-800€ bill, especially if multiple components need attention. Last question, should I avoid driving it until tomorrow, or is it okay for short trips if I stay light on the throttle?