Crankshaft position sensor

I recently had an engine light diagnosis of crankshaft position sensor. I replaced the part, and all seemed well with no problems starting, idling, or accelerating. But two days later and less than 50 miles since changing out the part. Its doing the same thing only worse. I took it to a part store and got the free diagnosis and again. Crankshaft position sensor! It has died several times after starting with a very rough idle. But then I can turn the ignition off and then on and it will start up and run fine. There seems to be no method to the madness (at least to me, a shade tree at best). Oh, when it starts rough, the tachometer does not work. Thinking maybe the fuse, I checked but it was fine. Any thoughts?