The repetition of the problem, and your troubleshooting so far, points to a possible restriction in the fuel system. The engine outruns its fuel supply - how is your fuel filter?

Next time you try, take the gas cap off to eliminate a venting problem in the tank.

Is your car full of fuel? - 700s are susceptible to holes in the fuel pick up - causing troubles when the fuel level is low - this often starts with a bit of trouble with smooth running when the level goes down.

Often this problem gets worse as time goes by. Our '88 745 GLE would start to act up at 1/4 of a tank - we kept the fuel up so well that about 2 years later, when it acted up, we almost forgot what the problem was. I have read of cars that would not run with 3/4 of a tank.

Basic troubleshooting theorem - Did something happen just before the trouble started?

In our case, I found a bad connector on our MAS right after Volvo did a tune-up - the tech unplugged it to put a new air filter in - then It refused to accelerate! - a pin got pushed back in the connector.