Desperate for help! My wife's car has 53k. It sat in the garage for 6 months. After the initial start, it was idling at 1,800 RPM. Worked a few weeks and the issue was the Idle Control Computer. I replaced it. It dropped the speed to 650-700 RPM.
Moving forward, it now has a rough idle. When we start the car it is idling at 700 RPM. It has irregular idle and black smoke. After driving a few miles, it's OK. I've drain the fuel & use 91 octane added Lucas. If I pull the wires off the Idle Control Valve it speeds up to 1,500 RPM.
What should I look at? I feel it should idle faster until warmed up.
Thanks for any assistance.

Hello - take a look at the link below to an earlier thread where this is discussed. Hope this helps you a bit and best of luck!

http://www.peachparts.com/shopforum/sl-forum/61242-fixed-rough-idle-380sl-steering-play-read.html