Les forums de la Peugeot 309 | The Peugeot 309 Forums

I always wondered what does the thing it the red circle do? Because it has 2 vacuum tubes, one connected to the cooling system and one to the thing in the blue circle.

Does it open the second air intake tube from above the exhaust manifold, when the engine is cold?

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I think it switches automatically how much fresh air form the front is taken in and how much got from behind the exhaust.

It helps the engine in cold starting. If I'm incorrect, somebody, please say so.

I was wondering too. Baptiste may now ("srdturbo")?

It's an air reheating system and the blue cap is a sort of air mixer which reinjects hot air within the system.