why does rpm rise and fall and then engine will shut down

Hello, when engine idle goes up and down, or a stall occurs, the first thing I imagine is that there is a fuel / air mixture concern. Too much or not enough fuel, too much or not enough air -- sometimes caused by an un-metered air leak, such as air getting into the engine when not expected -- causing a situation where the engine's processor keeps on trying to provide more and more fuel -- which can never be enough, and the vehicle stalls. Now, this is a guess, and this is not citing a specific place to look. But, clearly, either fuel, air, spark or engine timing / compression is a concern here, and warrants testing to determine what is going wrong.