High Idle in Park and Neutral

My 2001 Daewoo Nubira has had a high idle when cold and hot for about a month. When the engine is cold, like in the morning, I turn it on and the idle will jump to about 1600, sometimes it will drop to 900 sometimes it won't. I start driving and it's fine until I park it again, when I put it in park it will sometimes Idle at 900 but will usually jump somewhere in between 1600 and 2500, although it has gone as high as 3200. My first thought was the idle air control valve, so I took it out and the valve had some carbon buildup on the tip, but not what I would consider a lot. The hole had more so I used a cloth soaked in intake cleaner and cleaned them both. This didn't help, so after some research, I thought maybe a vacuum leak. I used propane to try to find the leak and while I was doing this I noticed two things. The first was the IACV made a grinding noise when the car was started, and when it was turned off. The second was after about 10 min of the engine idling at 900 I heard a pop and the idle immediately jumped to 1600. I don't know if either of those means anything but. Am I on the right track? What else could be broken?