Peugeot 307 Cold Start Rough Idle

Based on your description, a faulty cold start injector seems plausible. The poor running during cold starts strongly suggests a fuel delivery issue. Have you noticed a decrease in fuel efficiency or unusual smells? It might be worthwhile to investigate other fuel system components. Have you attempted an injector test?

I haven't observed a significant decrease in fuel efficiency or unusual smells, and I haven't attempted an injector test. How might one conduct such a test on the fuel system, or determine if the injection valve is defective? My knowledge in this area is limited.

I understand your concerns about performing an injector test yourself. Given your limited experience, it could lead to further complications or damage. While there are DIY methods, they often require specialized tools and a solid understanding of the fuel system. Since the injection valve could be defective, I recommend consulting a qualified mechanic for a proper diagnosis and repair to ensure the safety and optimal performance of your Peugeot 307.

I took your suggestion and consulted with a trusted workshop. They confirmed the injector was defective, and the repair was 515€. Thanks for pointing me in the right direction!