I have an '89 740 and sometimes (occasionally, but more often now), when I start it, it seems like its about to stall, the lights dim, and all the lights on the dash light up, then the RPM's bounce around under 1000.the engine sounds like its repetitively, and faintly reving. It gets better if I give it gas. But today it did it while I was driving, It almost died, then came back. Does anyone know what the problem could be?

Try This first. It at no cost to you. Re move the bottom engine cover and follow the ground cable and remove any tape. pull on the CABLE that is bolted to the ENGINE block and see if it moves or it just might come right off the connecter like mine did. If it does , buy a new 48" cable and re-route it , but NOT threw the frame holes, run it behind the power stering pump. Thats what happened to me anyway, same symtoms, Dan.
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Dans 88 740 GLE Wagon

it is possible you might be in the early stages of a distributer fail, if you have high miles and it has never been replaced check into it, but first do all the norm stuff turne up, clean throttle etc if all that doesnt fix it start looking at the dist as a possible. mine bother started going during first start and then merged over into driving.

Sounds as though you suffer from low idle. Clean your throttle body (instructions in the FAQ) as a start.