Adjust idle on 1996 Mercedes 220 4 cylinder gas engine

My 1996 Mercedes 220 4 cylinder fuel injection gas engine stalls at intersections because it is idling too slow. I cannot find a traditional type idle speed adjustment screw. Can you advise me on adjusting the idle speed? I found a thumbscrew type adjuster that goes around the end of the throttle cable, but when I turn it only slightly, the engine speeds up too much to around 14000 rpm, yet if I back it off slightly, the engine idle speed returns to a too slow idle speed. Currently it idles at only 6000 rpm. I'd like to boost it up to around 9000 rpm.