Neither symptom fits my situation. Butter smooth above 1200 rpm, idle is stable but shakey at 600-700 rpm with economy gauge reading half way in D with AC on.

The flapper thing inside the idle air valve moves freely and I don't think I can get it cleaner than it is.

Hoses look good. I've sprayed all around with carb cleaner and haven't found any leaks.

Argh!

Sixto
95 S420
91 300SE
87 300SDL
83 300SD