Honda City Engine Running Rich

Hey, I had similar symptoms on my City: reduced power, rough running, check engine light… sounds familiar. What's your fuel economy like? If it's way down, that points to a rich condition. Have you checked for any obvious fuel leaks or anything around the intake manifold?

Thanks for the quick reply. My fuel economy has definitely tanked; I'm getting about 20% fewer kilometers per tank than usual. I haven't noticed any fuel leaks, but I haven't specifically inspected the intake manifold. What should I be looking for there, and could that really cause the engine to run rich?

Well, a leak in the intake manifold can throw off the air-fuel ratio. The engine control unit (ECU) relies on sensors to determine how much fuel to inject based on the amount of air coming in. If there's unmetered air entering the manifold after the mass airflow sensor, the ECU will think there's less air than there actually is, and inject too much fuel. That being said, with those symptoms and the check engine light, I'd bet on a faulty fuel injector. It could be stuck open or leaking. I'd suggest a visit to a workshop.

Thanks a lot for the detailed explanation and suggestion! It was indeed a defective fuel injector. I took it to the workshop, and they confirmed the diagnosis. Replacing the injector set me back 515€, but the car is running smoothly again. I appreciate your help in pointing me in the right direction.