نشتی یا پوسیدگی شیلنگ خلأ

A rubber or plastic hose in the engine's vacuum or crankcase ventilation plumbing, split, hardened or pulled off its stub. Underbonnet heat cycles rubber thousands of times, and it ends brittle — so hoses that were flexible for a decade crack all at once, usually at a bend or where a clip grips them.

A leak here is unmetered air, entering after the sensor that measures intake flow. The engine burns a mixture leaner than it intended, corrects with fuel trim until it runs out of authority, and reports a lean fault whose real cause is a pipe.

On the crankcase ventilation side the consequence is different and worse: the system stops holding the crankcase below atmospheric pressure, and pressure that used to be drawn away starts pushing outward on the oil seals — which is how a split hose becomes a leaking crankshaft seal.

They are cheap parts and they are worth replacing as a set once one has gone, because they all aged together.