I have heard of the solder joints within the valve body cracking and needing a touchup with an iron. Also, check the throttle valve switch -- located right of the valve/3-pole connector threaded into the manifold. Job 07.3-121 in the service manual. This switch not closing can keep the idle high even if the valve and control unit are OK. See mbcoupes.com archives for more details. Cheers, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo