1986 740 sedan, In the morning, on my usual morning route, just as the car reaches normal operating water temp (about two needle widths to the cold side of vertical) just happens to be when I reach a relatively mild hill on the road. I'd have been running about two miles on flat ground, very light throttle, car shifting at 2500 rpm. When I reach that hill, apply just a touch more throttle, the car suddenly runs extremely weak. It is running smooth, no misfires, no bucking. Sometimes it just clears up on its own, sometimes I have to shift down, letting the rpm climb. It lasts for a few seconds, then the power comes back on. It comes back on pretty smoothly, again, no missing, no bucking. Sometimes it surges a little, but usually it is one shot and smooth. If you were a passenger you'd assume I just stepped on the gas.

Intermittent probably isn't exactly the right word. It can be reproduced pretty much at will, but the car has to start out cold, has to have set for several hours. Hasn't ever happened once the car is truly fully warmed up.

Any ideas?
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-rcf