YMsin, thanks for sharing.
Now I'm beginning to think that there might be a chance that the fuel pump is playing tricks. Perhaps its not fair to call it faulty, but rather more like what you mentioned - "the fuel pump not functioning as efficiently as it should, i.e. not delivering the kick when more fuel is needed ". Makes quite a lot of sense to me. Perhaps at higher loading, the fuel pump does lose some kick, and there goes the spoof-spoof.
And I also feel that this problem could be independent regardless whether its a 124 or 126.
Great! I'm waiting to hear your update next week! If you can do me a favour, could you ask your mechanic if my 1983 280SEL has an idle control relay? Thanks!
I'm not giving up yet!