What year is your 190d. I forgot even though the injection pump is mechanical some may have an external idle control system incorporated. This is unlike our earlier cars and I forgot about this.

Since the shutoff change initially seemed okay. Get a vaccum diagram of your set up and check it out. Or on the continued effort to repair the no key turn off you might find the issue as well. If you do not own a mity vac the cheap brass one from harbour freight will do well enough.