I had a weird experience with my 2015 Honda Civic that had me really worried, and I wanted to share it in case anyone else runs into a similar issue. About two weeks ago, my car started exhibiting these symptoms: the engine would idle roughly when I stopped at lights, there was a slight stumble when I accelerated, and sometimes a faint check engine light would pop on. At first, I assumed it was something serious with the catalytic converter, especially because a friend mentioned that a faulty cat could cause some of these symptoms.

Not being entirely mechanically confident, I decided to do some homework before heading to the shop. I started by checking for any obvious issues under the hood. I inspected the wires and hoses around the intake manifold, but nothing jumped out at me. I even used an OBD2 scanner (bought cheaply online) to see if I could get any more detailed codes, and it threw a P0171 code, indicating a lean mixture. That code seemed odd if it were just a catalytic converter issue.

After some online research and reading through a couple of forum threads, I learned that a P0171 code combined with rough idling could also point to a vacuum leak. I retraced my steps and decided to inspect the vacuum lines more carefully. It was then that I noticed one of the vacuum hoses connected to the intake manifold was a bit frayed and didn’t seem securely attached. I fixed the hose by reattaching it properly and using a small clamp to ensure it stayed in place.

After that, things got much better. The engine started idling smoothly again, and I even reset the check engine light (it didn’t come back on after a few drives). The initial thought of a major catalytic converter failure turned out to be a simple loose vacuum hose—a fix that cost me way less time and money than I’d have spent if I had gone to the dealer immediately.

My takeaways for anyone facing similar issues:
• Don’t jump to conclusions. Sometimes parts that seem expensive (like a catalytic converter) aren’t the culprit.
• Get an OBD2 scanner or have one handy; those codes can really guide your troubleshooting.
• A visual and careful inspection of all hoses and connections can often reveal something as trivial as a misconnected vacuum line.
• Spend a little time on research online—often, you’re not the only one with that problem.

I hope this helps someone avoid a trip to the mechanic if you face similar symptoms on your Civic or similar models!