Hello all,
My 450SL was idling rich after warmup, and after much reading I decided that a possiblity could be the warm up regulator. (The symptom observed was that I could push down on the airflow sensor plate and correct the overrich condition, but couldn't adjust it lean enough with the idle mix adjusting screw.)I removed it from the engine, unscrewed all the screws and nuts holding it together, and very carefully removed the bottom plate. I found a diaphram that is controlled by manifold vacuum, with an adjustment screw in the middle, that pushes against a spring which in turn pushes against the valve plate that controls the line pressure for the injector control piston. My thought was that I had too little pressure, so I screwed the adjustment in about .050. I then reassembled the warm up regulator, reinstalled it, and after readjusting the airflow sensor plate's idle mix adjusting screw it idles very nicely now. (Before, I couldn't get it to idle lean enough regardless of the adjustment.) This year CIS has no feedback, no O2 sensor. I did check out the heating element, it has 24 ohms resistance, seems good. When I took the unit apart, the bimetallic strip was still up away from the springs. (Hot condition)

My question to the learned folks here on the forum is: Did I do the right thing? I know this unit was calibrated carefully around 26 years ago, but I'm thinking that the springs might have weakened a bit as they aged. I'm thinking I should order out a CIS-K pressure gage set, I see them advertised for around 60 - 80 on a few websites. What should I see on the high pressure side of the warm up regulator valve, cold and hot? Would it be worthwhile to consider installing the pieces to add lambda control to the engine?
I am a newbie to the intricacies of the CIS-K setup. What is the purpose of the unit between the warm up regulator and the injection pump? It looks a little like a pressure regulator, but the vacuum control line is connected to the air cleaner on my car, so I don't think it could be regulating much. (update: after more reading I found the answer to this question, it is a pressure damper, and was removed in 1981 when they made the tecalan element in the control pressure line longer.)
Thanks for any illuminating answers you have!

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C