1973 still has electronic injection not mechanical. This means it has 4 trigger points in the distributer. The are a common problem. For this car to start idling rough and hard restart make me suspect leaking or dirty injectors. The idle airslide is adjustable for flow rate. Not for the typical DIY tinkerer without plenty of studying repair manuals. My 50 plus years as an MB mechanic gives me some insight on these older cars.
Another great, informative column. I was wondering what an "air slide valve" was (something for an amusement park ride?) Now I know. I've occasionally had issues with an idle air control valve, so I'm familiar with the symptoms. Those older Mercedes models still look fantastic.
This sounds like the perfect time for an LS Conversion... Oh I'm only Joking. Just a little nudge to the real MB fans out there to gently needle them out of their slumber. Of course, they might be far more gentrified (or is it petrified?), for such a subtle tweak to their MB-hood to arouse them. 🙂 Really, my first thought was if the car was just a bit newer and the slide valve was electric; the headline could've been "When the Disco air valve loses it's Electric Slide", but I have issues. 🙂 For expertise; I bow to the long term MB mechanic. Though, I would think a dirty air valve could cause those problems also. Given the quality of today's fuels and their lack of stability, the larger causation might also be fuel related. Perhaps after cleaning the air valve and more if that's not all of it; regular use of Sta-bil or Sea Foam, in the fuel, could help keep those problems at bay indefinitely. That and putting more miles on that wonderful car wouldn't hurt either. They were built to be driven.