Sounds like were all in the same boat regarding the high idle and stalling with our beloved (ha) 16v`s.
If you go back over some of my prior posts, you will see my unending journey. I also had the mystery vacuum leak that I couldn`t find. It really caused a problem after I cleaned the throttle body with carb. cleaner. The idle shot up to 1500 and would not come down! I ended up removing the whole injection manifold and resealing it with new gaskets and hoses. The result......no big difference! AURGHHH!!!!
But...... I finally got my idle down to a normal level after playing with it for a few WEEKS. But now I have a stalling issue
Here is what I want you to do. When it starts to idle high, check the voltage or duty cycle at the X11 plug #3 pin on the drivers side inner fender. Tell me if you see a fixed or fluctuating voltage.
I think this might steer both of us in the right direction. I want to see if you readings are the same as mine.