this use to happen just once in a while but now it happens all the time
my 91 turbo just stalls out for no apparent reason,no missing, no sputtering , on 1991 Volvo 940
It's very common for these to have a bad fuel pump relay or fuel pump cause a stalling while driving issue. Take this to a volvo specialist and they should be able to easily figure it out. If you're going to fix it, replace the fuel pump relay and see if that helps.
seek diag and est from your mech