Skoda Praktik fuel consumption and hissing sound

That sounds like a classic air intake leak. I had a similar issue with my Renault Megane a few years back. High fuel consumption, check engine light, and a hissing sound are all telltale signs. When does the hissing happen? Only on acceleration?

Yeah, the hissing is only when I accelerate. Could it be something more serious like the intake manifold itself?

While it could be the intake manifold, a cracked hose is far more common, especially on older vehicles. The increased airflow from acceleration puts stress on the system, making leaks more apparent. Issues with the throttle body can also cause hissing. An engine misfire is a potential symptom of an intake leak. I would recommend you take it to a workshop. They can do a smoke test to pinpoint the exact location of the leak. It is also safer than experimenting yourself.

Huge thanks! I took it to a mechanic, and you were spot on. It was a split in the intake hose, just like you thought. Replaced it, and the hissing is gone, the check engine light is off, and the fuel consumption seems normal again. Total cost was around 100€ including labor. Appreciate the help!