I'm having rpoblems with my '87 230e. Cold idle is low as if there is no high speed idle system. I did some research and played around without much success. What I did find was:The rotary actuator is driven by the ECU. At cold start the ECU sends 12 volts to it and it opens an internal passage for air to bypass the throttle body and hence raise the RPM. When the engine has warmed up, the actuator (on mine) was only getting 2 volts and was nearly closed as I expected. It's supposed to control fast idle during warm up, and idle speed under load, e.g. with air con or power steering actuated. I pulled the top hose off and put 12 volts to it and you could see the actuator work. Even so, mine won't idle properly when cold and when you put the air con on the idle drops. Out of curiosity, with the engine running I carefully moved the air hose to the actuator around to make it leak. Sure enough, the revs went up. So I don't know what's going on. The rotary actuator seems to work but it's not controlling the idle properly.