The TH fix is simple to do and will cost less than $1. You may have to experiment with different size holes. You will want to disconnect the battery for about 10 minutes to reset the computer. This might also help to clear up your low idling problems.
If the TH fix doesn't work, it may be the IAC valve, throttle body, or throttle positioning sensor. Agree with the statement about the cleaning. I've suffered from severe throttle hang (throttle rise is more like it) in the past, and have ended up replacing the IAC valve, throttle body, among other things. Seems to be a recurring problem. We'll see...
Can't help you on the issue with the secondaries.
