Air slide valve?
I changed my "air slide valve" which is a little air pump that smothes idle on the M117 motor. If it doesn't operate at idle it could be bad or the controller could be bad, or both. I think you can check it for voltage. Do you have the manual? Sorry that I don't know your motor better.
I changed the valve and controller. Had a ICU problem that was the final culprit. I assume you have been through the primary ignition.
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si