intermittent stall at idle

My friend has 90 Lumina 3.1L engine. He has an intermittent stall at idle and sometimes an intermittent miss at highway speed. It always restarts after stall, you can't check for lose of spark. Wires and plugs are good. He thinks it's a crank sensor, I don't. I have the same engine in a different model, I replaced my crank sensor, a while back, but my symptoms were totally different. Do you folks think it's the crank sensor? thanks