Before you start buying parts, take the time to figure out exactly what is going on and when,, so that you can diagnose the problem.
You posted that this is an 85 euro 500sl, right? When you start it "cold" does it start right up but, run like crap, stumble and belch "black smoke" when you try to give it throttle? After it runs for a couple of minutes, does it seem to "clean up' and run OK?
If this is what it's doing, that usually indicates a problem with the "warm up (or fuel enrichment) regulator".
Orrrrrrrrrr, does it idle bad all the time cold & hot? How easily does it start? Details etc.