Date registered: Jul 2008
Vehicle: 82 380SL 96 SL500 03 SL500
Location: Southern Illinois
Mentioned: 1 Post(s)
Quoted: 264 Post(s)
The screw you push down meshes with the idle mixture adjustment screw as shown in the pic Pete posted. It pops up to keep you from causing damage when pressing the throttle with the adjustment tool engaged.
Note that it is an idle mixture screw and not an idle speed screw.
If it doesn't fit, force it.
If it breaks, it needed replacing anyhow.