Since I got my 16v, the IACV has been unplugged. As soon as I plug it in, the engine won't hold an idle. If it's idling and I plug it in, it just shuts off.
So, to investigate, I took the airbox off and watched the AFM plate. As soon as the IACV was plugged in, it closed, cutting the air from the mixture, and obviously killing the engine.
I've taken the IACV out and cleaned it thoroughly, and tested it by running voltage to the poles - it opens and closes fine.
How can I stop it doing this?! I'm thinking vacuum leak somewhere? I changed the moulded rubber hoses to it (they had got old and gone hard), but no difference.
Help! This is driving me nuts!

1989 190E 2.5-16.