Subaru Stella Engine Losing Power After Recent Repairs

Had very similar symptoms on my 2004 Subaru Impreza. The check engine light kept illuminating and the engine would surge and lose power, especially during acceleration. After multiple diagnosis attempts, it turned out the fuel injectors were failing, causing an incorrect air-fuel ratio. The symptoms match what you describe, rough running, drop in power, and lean conditions. When fuel injectors start failing, they often dont spray fuel properly, leading to incomplete combustion. The oxygen sensor readings were all over the place, confirming the lean mixture. In my case, two fuel injectors needed replacement along with cleaning the intake manifold which had carbon buildup from the poor combustion. This was a serious repair that required removing part of the intake system to access everything properly. Since youve already replaced the spark plugs and MAF sensor without solving the issue, failing injectors are a likely culprit. Would strongly recommend having the fuel injection system properly diagnosed with specialized testing equipment. The symptoms align too closely with a fuel delivery problem to ignore.

Thanks for sharing your experience with the fuel injectors. I dealt with almost identical issues on my Stella last year, the check engine light, rough idle, drop in power. The EGR valve was actually stuck open on mine, causing similar lean conditions. Getting the valve cleaned and replacing the intake manifold gaskets fixed it completely. Has the problem come back at all since your repair? Also wondering roughly what the total cost was for replacing those injectors? Always good to know what to expect price-wise for these bigger jobs.

Just got back from having this issue properly diagnosed and fixed. The symptoms completely disappeared after replacing a faulty fuel injector that was causing the lean fuel mixture. Total cost was 515€ for parts and labor to replace the defective injector. The repair shop confirmed the fuel injection system was running way too lean, which explained the rough running and check engine light warnings. Since fixing it two days ago, the engine runs smooth with normal power delivery and no more jerking during acceleration. Unlike with the previous spark plugs and mass air flow sensor replacement, this fix actually addressed the root cause. Getting the fuel injectors tested was key, faulty injectors can mimic all sorts of other issues. The catalytic converter was also inspected but thankfully wasnt damaged from the lean condition. Its been about 6 months since the repair with zero issues. The engine maintains proper fuel delivery and runs exactly as it should. If anyone else experiences similar symptoms, definitely have the fuel injection system thoroughly checked.

After dealing with those engine problems for weeks, I finally got it properly diagnosed and fixed yesterday. The throttle body was heavily contaminated and the EGR valve was completely stuck, causing the lean condition. Total repair came to 380€ including cleaning, parts, and labor. The mechanic showed me the gunked-up components, no wonder the engine was running so poorly. They cleaned the throttle body, replaced the EGR valve, and checked the catalytic converter for any damage from the lean running. Fortunately, the cat was still in good shape. The previous repairs replacing the spark plugs and mass air flow sensor were unnecessary since they werent actually the problem. At least now I know what was really causing the issues. The engine runs perfectly smooth with normal power delivery and no more check engine lights. Really glad to have this sorted after weeks of frustration. Thanks to everyone who offered advice and shared their experiences. If anyone else runs into similar symptoms, definitely have the EGR system thoroughly inspected before replacing other parts.