You described, perfectly, a problem I had with a (purchased new) '73 164. When it first started happening (still on warranty, thank g-d), it baffled the dealer (they held it for two weeks trying to figure it out), but they eventually had to take the car up to Rockleigh headquarters. There the techs discovered that this was a typical symptom of their new (at that time) type of EGR valve when it failed (got dirty or something). Note that I'm not talking about a flame-trap -- on my '73 164 there was an actual mechanical valve, and when it clogged it would make the car stall whenever I stepped on the brake to slow the car rapidly (apparently, the EGR valve was supposed to redirect something to lessen emissions on rapid deceleration, if I recall what they told me).
So, if your 140 has the same system as my 164 of the same year (I don't know if you do have the same system, but it's a possibility, isn't it?)...

...the cure is simple -- replace the EGR valve (it can't be cleaned, I was told).
Good luck -- hope this helped.