Koleos Stalling Due to Ventilation Valve

It's possible. A malfunctioning tank ventilation valve can definitely trigger those symptoms. The engine control unit (ECU) monitors the fuel tank pressure using a pressure sensor. If the valve isn't venting properly, it can create a vacuum or pressure buildup in the tank, messing with the fuel-air mixture. This leads to the check engine light and stalling. Have you checked the hoses connected to the valve for any clogs or kinks?

Clogs in the hoses, you say? Where exactly should I be looking for those?

Okay, so the ventilation system usually includes hoses running from the fuel tank to the charcoal canister (which absorbs fuel vapors) and then to the engine intake. Carefully inspect all these hoses for any signs of cracks, kinks, or obstructions. Even a small blockage can disrupt the system. Given the age and mileage, it’s plausible. That being said, without proper diagnostic tools, it is difficult to be 100% sure. A workshop might be the best bet.

Thanks for the help. Turns out the hoses were indeed clogged. New valve and hoses, cost me 175€, and the problem is solved.