Infiniti QX4 4WD light comes on while driving, car stutters and stalls

So, awhile back I had to drive in some icy conditions. I used 4WD for this, and have never actually used it before (bought this car from a friend almost 2 years ago). I followed the directions properly for putting the car into 4H AUTO, though I didn't switch to it while the vehicle was moving, I was parked with the engine running. It seemed to work fine.

A few days after this my car is running very strangely; it started with the RPMs dropping all the way to 1 anytime I take my foot off the gas, even If I'm going 80 MPH! So of course, when I put my foot back on the gas the engine revs hard all the way back up to the RPM it would normally idle at when driving that speed. After about 2 weeks of that, the car is now stalling sometimes when I come to a stop, and it stutters and misses incredibly bad at certain speeds/RPMs/whenever it feels like it.

Also, the 4WD warning light comes on and the back tire lights on the dashboard diagram go out (no-wheel drive?) shortly after I start driving. It's gotten so bad I can't even drive the car anymore, as I'm afraid of making it worse or causing some other problem. Any idea whats going on? I'm not sure if the 4WD warning light has anything to do with it.