تسرب من جلدة صمام التطهير

The purge valve passing vapour when it should be closed, through a failed seal rather than a stuck mechanism. The distinction matters because the valve still operates correctly on command — it opens, it closes, and it leaks slightly the whole time.

A small continuous leak has two separate effects and they point in different directions. It admits vapour into the intake when none was commanded, which is unmetered fuel and skews the mixture at idle where the leak is proportionally largest. And it breaks the sealed-system leak test, so a small-leak code appears with no leak anywhere in the tank or the lines.

That combination is the signature: a small evaporative leak together with a rich condition at idle, and it is worth recognising because each symptom alone sends the diagnosis somewhere different. Test the valve's ability to seal rather than its ability to switch — apply vacuum to it closed and see whether it holds, which a click-test cannot show.