Volvo Repair: 1998 S70 T5: Frigid weather: Engine stalls under load at startup, weather max, weather engine

Question
Hi,
My car:
Volvo S70 T-5 (stock turbo)
1998 model year (1997 in-service date)
155,000 miles
Automatic transmission
I only use supreme grade octane exclusively
Factory recommended service always followed very precisely.

On cold morning (ambient temperature is btw +7 deg F to minus 13 deg F), and I start my car, I let the engine free idle for 30 seconds for oil circulation. I gently shift into "D" after this period elapses.  This has resulted, on some occasions, in an immediate engine stall.  (I had to restart, rev slightly above idle and wait another 30 secs to prevent stall when placing back in gear). This has never happened before even though I followed the same exact cold weather start-up routine in the past. Is There A Particular Part That May Have Degraded And Needs Attention?

Please note some other pertinent information:
Problem is intermittent [for example, sometimes at -5 deg F it will happen and sometimes it won't]
The compression is within specs. I had it checked by the Volvo dealer.
The engine ALWAYS delivers a reassuring positive healthy start even on those particular days when it stalled after placing in gear.
I drive very gently (rpm below 1800) until engine reaches normal temp in order to warm up engine components. I never allow prolonged free idling in cold weather at start-up since owner's manual advises against this action in frigid weather (max 30 seconds allowed by owners manual when temp is below 5 deg F). The throttle body was cleaned by the dealer (which appeared clean already) but this did not help since the problem repeated after as well. I have oil consumption at rate of 1quart every 1200 miles (but there is never any smoke from the exhaust even at start up).
I have very good mgp numbers. Comparison of readings from the car's digital fuel consumption indicator against my other 3 cars (they are sport sedans as well) have repeatedly shown that the Volvo provides the best mpg even though this car is older and faster than them. The oxygen sensors have never been replaced.

Your input will be appreciated.
Thanks.
Ghassan.  

Answer
Greetings,
          Thank you for such a detailed history...I also use only permium fuel in my cars  ...many good reasons to use it...including...fuel related system are in much better service when mileage is high...including throttle bodies,cats and injectors.
         I wish I could point you to an exact reason for the stalling problem.
          If the problem has caused a imbalance it will be read on computer code test equipment..found at dealer or other modernized repair shop.
         I'm surprized that the oil consumption is a qt.each 1200 mi...it could be related to stalling...oil drips into cylinders overnight and screws up the fuel charge properties when started in morn.
           
          Good luck,
                   Bilbo