Recently, my check engine light came on and my car began to stall when stopped in "drive". I changed spark plugs, fuel filter, and then found a hole in the hose connected to the PCV valve so I replaced that. It no longer stalls in drive, but the engine light is still on and it has begun to stall when I put it into "park", particularly if the AC is running.

First thing to do is have the codes read. Then you can begin to accurately diagnose your problem. Go to autozone, they will read them or free. then post the codes here.