As was mentioned, your problem sounds pretty characteristic of an "old age" fuel injection relay. We went through this exact same random stalling with my wifes 91 740 and my fathers 90 740. Look in the fuse compartment above the console. You'll have to pull the small panel to get in there by prying off the ring around the lighter that will reveal a screw. Once inside, you'll see several rows of relays behind the fuses. I'd guess the FI relay is the tall (usually) white one on the left of the second row. Pull it out and remove the cover. You can inspect all the contacts on the underside of the circuit board with a magnifying glass looking for a subtle crack(s) in the solder joints that are usua;lly circuliar. Chances you'll find more than one broken joint but even if all looks well, I resolder it anyway. You can resolder the joints with a small iron or pick up a new relay that isn't that cheap but won't hurt your wallet that bad (I'm guessing $ 30-40.).