I've had the same experience with my 95 16v. My past experience with idle screws is pretty much the same as yours, minor movement, immediate results. The wording in the service manual leads me to believe there is no direct connection between the idle screw and the butterfly, the connection is made electrically, and you are actually turning a potentiometer. The service manual also states ( this is for a 95 16v 0nly, as it's the manual I have) you need to use a diagnostic scanner to get the correct setting, as it's a matter of setting the pot correctly. Not having the diagnostic tool, I just kept trying a bit more turn, start and run till warm, repeat until I got It where I needed it. It still fluctuates sometimes, drops down as low as 600, but idles back up again after a couple of seconds. Good luck.