Check Engine Light & Revving down while driving

I have 1996 Grand Cherokee Laredo(150k miles) that started acting weird about 6 months ago. Driving along the highway at 70mph the check engine and check battery light came on and the engine shut off. I replaced the crank shaft sensor and the car was working fine for a couple of months. Then it started to rev down while driving. At first it was every 10 minutes or so it would rev down for only a second or two, but each day that I continued to drive it it became more frequent until it happened every 10-30 seconds and then the battery completely drained and battery light came on and check engine light. I recharged the battery and when I turned the car back on, all the codes were gone and it was no longer revving down. It worked fine for another month and then it just started to start revving down again. I stopped driving it immediately. I recharged the battery even though it did say the it was low, but it didn't help this time. (I am starting to notice that this usually happens after it rains, but that might just be a coincidence)

I've seen online that some people clean the IAC, but that is only when the check engine light does not come, and every time this happens my check engine light comes on.

I am not sure what to do next. Any suggestions?

Check Engine Light & Revving down while driving