I have a 91 745 Regina with 215K miles on it. About a year ago it started to take a few times to get it to (cold) start in the morning. Later the car would still start this way, but the idle was a little low and I had to pump the pedal a few times to clear it. It would start on the first try when warm. But the idle would sometimes drop when sitting at a light with the A/C on. All in all, though, the car seemed to run fine, but it bugged me that I was wearing out my starter every morning. BTW, the fuel pump, pressure regulator and fuel filter had been replaced 5 years ago at 145K miles.

Then, one day the car wouldn't start. It would try to run, cough and die. My trusty 740 had left me standed for the first time in 17 years. Very unsettling.
Diagnostics were all normal. Nevertheless, I went ahead and replaced the fuel pump relay behind the ashtray and radio supression relay under the hood by the left strut tower. Still no go.

Bought a new fuel pump and put it in. Problem solved. Starts right up on the first try cold or hot. Idle is fine under all conditions.

I bench tested the old pump with a battery on the terminals and it still pumps. But I guess it didn't pump enough to 1) start the car properly and 2) eventually degraded so the car wouldn't start at all.

So you might consider the fuel pump a suspect.

Regards
Bill in PHX