Q: Will a bad or clogged EGR valve stall an engine and prevent it from starting?

The EGR valve is designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. When you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases. Once the engine reaches operating temperature and speed increases, the valve, either through vacuum or electronic control will gradually open, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. When the EGR valve is clogged or dirty, as they are prone to, it may not function properly causing the engine idle rough, stall at idle speeds, cause the car to get poor fuel mileage, or emit a strong smell of fuel due to excess hydrocarbons which also results in failing emissions tests. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.