Clio Hissing Noise Acceleration

That sounds familiar! I've got a Clio too. A similar thing happened to me a while back. That hissing noise is a classic symptom. Have you checked the intake hose that runs from the air filter to the engine? Those things can crack and leak, especially with age and heat.

When you say 'intake hose', are we talking about the big, corrugated plastic tube? And how did you pinpoint the leak? Did you just visually inspect it, or is there some kind of secret technique?

Yep, that's the one! The big, corrugated plastic tube. As for finding the leak, I initially just gave it a good visual check, but couldn't see anything obvious. It wasn't until I started the engine and had someone rev it a bit that I could actually hear the hissing clearly and feel the air escaping. Honestly, unless you're super confident, it might be worth getting a mechanic to take a look. Could be something else, and messing around with the turbocharger (if you have one) without knowing what you're doing can be a costly mistake.

I took your advice and booked it in at a garage. Turns out it was exactly what you said – a split in the intake hose! Cost me 100€ to get it replaced. Fuel consumption is back to normal, the hissing is gone, and that check engine light is finally off. You're a lifesaver!