Non-TDI Questions: Everything You Need to Know

Hi everyone, I hope it's not too much to ask if I have a question about a Corsa, since no one seems to know anything about them in the Opel forums, and maybe someone here is familiar with them. If this topic is too disruptive, you can close or delete it, but I'll start anyway:
I have a Corsa B 1.4 (X14SZ) with 60 horsepower.
'This air filter has a valve that can switch from cold air to hot air gradually, using a vacuum actuator. A (red) hose (vacuum) connects to this actuator. Logically, when the engine is off, there is no vacuum in the hose, so the valve is set to cold air. When the engine is running, even at idle, there is a vacuum in the hose, and the valve is set to hot air. I recently tested the system when I got the car, by giving it gas and observing the valve's movement. It opened further with increasing engine speed, and then returned to the hot air position at idle, which seemed normal. However, recently, I've tested it several times, and no matter how much I accelerate, the valve only opens a very small amount, perhaps 10% cold air. Now I'm trying to figure out how the system works.'
The vacuum hose connects to the throttle body. Next to it, the same hose continues in brown to the central fuel injection system. [Next to that, there's another hose that goes to the fuel tank vent (I think), into a box with a connector, and from there, another hose to the fuel tank.]

Well, maybe someone knows how it works and whether it's normal, or if it has something to do with the temperature that the flap no longer opens.
Okay, here's the translation:

'Or maybe someone will tell me in which book or website this is explained.'

Best regards,

Normally, the valve should direct warm air to the cold engine to help the catalytic converter reach operating temperature faster, making the car drivable sooner and warming up more quickly. When the engine is cold, a significant amount of warm air should be directed from the exhaust manifold; when the engine is warm, none should be.

'These vacuum reservoirs tend to corrode. Try removing them and possibly cleaning them (I'm not very familiar with Opel vehicles). Otherwise, replace them and check all vacuum hoses for leaks and proper seating on the connection nipples.'

The valve works perfectly; when there's a vacuum, it fully opens, but if there's no vacuum, it opens completely. That's how the control system works. If there were any issues with the vacuum hoses, it would behave the opposite way: it would stay almost completely open. I've been told that the flap is supposedly always open in idle mode, using hot air (for its function), but I couldn't get any more information.

I only remember this from my Golf2 GT. The canister was located there, and when the engine was warm, it allowed too much hot air into the intake manifold, causing the idle to become erratic. The correct setup was to have the canister completely closed once the engine reached its operating temperature, regardless of how warm it was outside.

"In the past, both Opel and VW vehicles had a small box located on the underside of the air filter: a thermostat valve. Does the box open when you remove the hose?"

Yes, I already wrote that.
It's good to know about the thermostatic valve; maybe I have one too.

Where can I find information about this system, or how to control it? There must be somewhere where this information is available.