It does sound like a vacuum problem and although diesels use vacuum for some different reasons other than gassers, and visa-versa, your CD manual will list what inches of vacuum is neccessary. If it leaking vacuum, it'll show up on a guage relative to specs, of course.

Just thought I'd mention one cause for reasons for lost vacuum that's not listed in any manual!

My 190E also had a vac leak and produced similar issues as your 124. Seems vacuum leaks are very common and a good place to start looking. Beyond that, it's another ball game!

BB