There has been a lot of discussion on this topic already but mostly wild guesses and talk of little technical substance. I was very annoyed by the rev hang in my new Toyota so I took deep interest in it and spent time to look at the issue at some depth. I believe I devised a solution. My findings are quite lengthy (with graphs and videos, over 10 pages long when printed out), so I placed them in a simple webpage located at http://www.revhang.altervista.org You are invited to read it.