I recently bought a 1990 745 Turbo. Second day I owned it it stalled on me 5 times - the Previous Owner was very decent and offered to split with me. Turned out to be the Fuel Pump Relay and the mechanic also did the Radio Suppression Relay. (Code was 1-4-4) Stalling stopped, but another problem that was harder to diagnose was:

Severe Hesitation on acceleration and load mainly, and only noticeable when WARMED UP.

Drove the car for a couple of weeks, during which in frequent mountain driving I noticed severe retardation of power, even as boost was occurring, and especially frequent when under load (going up a mountain) or accelerating on level on the highway the highway (esp. between 2400 and 3100 rpm). The loss of power would typically last one or two seconds, but repeated sometimes in rapid succession, more often as condition degraded. Thought it was Fuel Pressure Regulator but mechanic said usually see black smoke with bad FPR, thought probably O2 sensor or Air Mass Meter. Finally Check Engine light came on - was O2 sensor! Seems fine now - it was really happening a lot for two days before the light came on, but I do a lot of mountain driving. I took it for a good hard half hour highway and hill ride and it's gone! (But we just did it today.) Bad O2 sensor will give too lean mixture. Can be tested without code. I WILL update if it turns out not to be a red herring, but I can tell it's gone.

I thought this might help because the '89 / '90's are apparently really prone to having quirky computers in terms of throwing codes, and hesitation is one of the hardest things to diagnose. The pattern was established for two weeks before the light went on, but became much more frequent for the last two days. This car has new fuel pumps also within the last 30k miles, which did eliminate that option of diagnosis more or less.

Hope this helps.

Baba
1990 745 T 177k
1979 245 approx. 250k