Q: Diagnostics show the EGR and idle air control valve - what does this mean?

The idle air control valve is a unit that monitors the air intake into the engine as it is mixed with fuel prior to entering the motor. When this is not working properly, this will cause an imbalance in the air/fuel mixture causing the car to idle rough or stall at low speeds. The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it’s a simple valve that closes and opens as needed.

The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering. Whenever 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.

If you slow down sufficiently or come to a stop, the valve gradually closes and blocks the flow of exhaust gasses. After you shut off the engine, the EGR valve closes and remains in that position. 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, emit a strong smell of fuel due to excess hydrocarbons which also results in failing emissions tests. I would recommend having a professional, such as one from YourMechanic, come to your location to properly diagnose and repair the EGR valve.