When the engine is cold, the engine runs itself at a high idle to reach a more fuel efficient, warm engine temperature. Once reached, it lowers itself to a slower idle. Soon after, you rev the engine and step on the clutch letting the engine idle down quickly with the load of a compressor weighing on it which is a bit like having a extra dead cylinder in the engine. The idle drops quickly and the momentum carries it into a stall. Actually this is the same thing that the other poster was saying but in different words I guess. Another scarier possibility is that your engine is wearing out and has little compression in the cylinders and so is overwhelmed by any extra load.