Subaru R1 Rich Fuel Mix Issues, Common Causes & Fixes

I had similar symptoms with my 2006 Subaru R2, and after some initial troubleshooting the check engine light helped identify the root cause. With some experience working on cars, I first checked the air filter and intake manifold for obvious issues but found nothing unusual. The workshop diagnosed a faulty fuel injector that was causing the rich mixture problem. The excess fuel was leading to poor fuel economy and the jerky acceleration you described. The repair involved: Complete diagnostic scan, Fuel injector removal and testing, Replacement of one defective injector, System pressure testing, Test drive to confirm fix Total cost was 515€ for parts and labor. The symptoms completely cleared up after the repair, and fuel economy returned to normal levels. To better assist with your specific case, could you share: current mileage on your R1, When was the last time you changed the air filter, Are there any other warning lights besides check engine, Have you noticed any unusual exhaust smoke color, Did the symptoms appear suddenly or gradually This information would help determine if your issue matches what I experienced or might be caused by something else.

Just had my 20661 KM service last month. After reading your detailed reply, I am now suspecting it could also be a fuel injector issue in my case. The check engine light and poor fuel economy started about 2 weeks ago, quite suddenly. Have also noticed black smoke from the exhaust, which further points to a rich mixture problem. The oxygen sensor could also be at fault since these symptoms showed up right after I had my spark plugs replaced. Will get it properly diagnosed, but your experience really helps narrow down the likely causes. Thanks for breaking down the repair process and costs, gives me a good baseline for what to expect.

Thanks for sharing those additional details about the timing and symptoms. Since my R2 had nearly identical issues, I should mention that black exhaust smoke combined with the sudden onset strongly points to a fuel system problem rather than an oxygen sensor. The intake manifold and fuel injectors should definitely be the first items to check. In my case, the faulty injector was stuck partially open, dumping excess fuel that caused the rich mixture and black smoke. Having this fixed early likely prevented damage to my oxygen sensor and catalytic converter. One quick test you can try: let the engine idle for a few minutes and see if the black smoke gets worse. With my defective injector, the smoke would become more noticeable during idle since unburned fuel would build up in the system. The timing right after spark plug replacement is interesting but possibly coincidental. The fuel economy issues and black smoke are classic signs of a rich mixture caused by fuel delivery problems rather than sensor issues. Based on your lower mileage and the sudden symptom onset, I would bet you are dealing with a similar injector problem rather than a worn oxygen sensor, which typically degrades gradually over time.

Thanks for sharing more details about your injector repair experience. Having those symptoms show up right after the spark plug replacement does make me wonder about the timing. The black exhaust smoke I am seeing definitely confirms the rich mixture issue you mentioned. My car has relatively low mileage at 20661 KM, and everything was fine until 2 weeks ago when the problems appeared suddenly. The last service was just done recently where they changed the air filter and did other routine maintenance. Besides the check engine light, there are no other warning indicators. Will get it properly diagnosed but your experience with the fuel injector repair is really helpful to know about. The repair costs you shared also give me a good idea what to budget for if it turns out to be the same problem. Going to have them check the intake manifold and run tests on the fuel injectors first before looking at the oxygen sensor, since the symptoms match what you described with your faulty injector. Just hoping to get this resolved quickly before it potentially causes issues with other components like the catalytic converter. Will update once I know what the actual problem turns out to be.