I drive a 1992 745, which replaced my 1987 245, which replaced my 1984 Diesel 245 wagon.
All went well until it needed a head gasket. After the $1650 job, which was done well, I drove through a big rain storm. The car stalled and took 15 minutes to restart. I figured there was water in some circuit, like high voltage. Drove it four days after it dried out. No problem. Then in warm sunny weather it stalled out and could not be restarted. After the fix, it idled roughly and stalled on acceleration. At 750 rpm or higher it ran like a champ.
My independent Volvo mechanics could not find any error code. They replaced: High voltage pack (its a Rexx Regina), distributor cap, high voltage wire from coil to distributor, fuel pressure regulator. Problem returned within a few days. They replaced engine temperature sensor. Problem persisted. They checked the fuel rail and injectors. No fault found. I replaced the idle air motor. They checked and cleaned the throttle body and microswitch. I cleaned the manifold air pressure sensor and the air temperature sensor.
Problem persisted. I found that a bottle of Gunk Fuel System Cleaner would smooth out the idle for a while, then back to running rough and stalling.
I ran an an auxiliary ground wire from battery negative to every ground point on the block and chassis. A few stray electrical problems vanished, but the stalling persisted.
Finally, six months later, i couldn't keep the car running at idle. It would stall in the middle of a street. Bad news. Limped back to my Volvo mechanics with the instructions "keep the $#%^&*thing until its running right." I thought about buying another 245.
Still no error codes. Finally, we all got the brilliant idea to check the oxygen sensor. It was the original OEM sensor from 1992. Replaced it. Problem vanished. I insisted on changing the fuel filter just for good measure. It was the original also.
Moral of this expensive story: Not every problem in this model shows up as an error code. If you experience the same flakey problem, start with the oxygen sensor which lives in a very harsh environment.
The good news: I get to keep my 745, which still runs like a champ and holds more stuff than a 245 with greater handling and comfort,