MK4 2.2L Engine Malfunction P0299 - Only Occurs on Cold Morning Hills

Hello, I'm experiencing a specific issue with my 2008 MK4 2.2L 175 HP Ford vehicle. When the engine is cold—typically in the morning—I notice the 'Engine Malfunction' warning light activate only when driving uphill on my commute to work. The car runs perfectly under normal conditions; I don't feel any loss of power, hesitation, or performance issues during regular driving. The problem does not occur during daytime drives or when the engine is warm. A diagnostic scan revealed fault code P0299: 'NOT ENOUGH AIR IN THE INTAKE SYSTEM'. I've taken the car to a mechanic, but they're unable to pinpoint the exact cause. This issue appears exclusively in cold conditions and only during uphill driving. As a vehicle owner with limited technical knowledge, I'm seeking advice on how to investigate or resolve this problem. Any insights into potential causes—such as intake system leaks, vacuum hoses, or throttle body issues—would be greatly appreciated. Thanks for your help! Vehicle: MK4 2.2L (2008), 175 HP