Q: Rough idle and engine stalls out.

This suggests a rich fuel condition as evidenced by the black fouled out spark plugs. This can happen for a couple of reasons such as faulty or leaking fuel injectors, or a faulty or dirty idle air control valve.

The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. As this valve is controlled by the vehicle’s computer, it will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.