If any of your idle air or breather hoses are shot, replace them all. As long as there are air leaks, any other troubleshooting will be useless. Check all vacuum lines too, and replace any of the rubber couplers that show aging. All this is detailed in many posts here, as well as more complicated issues when these are resolved.
MB uses lots of rubber, compared to Japanese cars of similar vintage. Be prepared to replace most of it on an '85.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7