Hello all, was wondering if anyone can help me with an issue im having.. My 79 450SL idles around 1200rpm's while warming up..Takes like 30 minutes of running for it to come down..I have been putting air conditioning on just to kick compressor on to slow it dow so it dont slam into gear.. I tried adjusting that big white nylon looking scew but I can actually screw it all the way in without much effect on slowing down idle..Is there an idle speed control or something in this car? Am I supposed to be able to stall car if that white screw is turned all the way in? If so what would I need to replace in that instance? Thanks for any and all suggestions...

Sounds like vacuum leak . Check all the small bore vacuum pipes that you can,and you may find one thats not connected .. Do you have an air control valve on your engine. Take it out and soak it in white spirits .Dont drop it right in the fluid to clean it as it as electrical plug on the rear. Spray it with carb cleaner and leave it over night .

Hello Optimus, now is the air control valve the thing that the idle air screw is part of? I looked up some info on that ..Is that the thing that has almost like a thermostat inside of it and it changes the idle speed depending on engine temp? Thanks for your help again..I think you helped me with my last question about fuel injector seals too..

1971 i think so ..It wants cleaning out with carb cleaner.Or better still white spirits ,put some inside and shake it around while holding the other outlet hole .Check that the hoses ,2 of them are connected to the engine and not split .Have you checked out the tech info top of this page it as lots of info on the site.