I once had a similar problem on my NA 88 740 which had the same engine and set up as yours. It was caused by collapse of the bellows tube leading to the throttle body. When I gave it a lot of pedal it would collapse, this in turn cut off air flow to the throttle and created an unusual vacume in front of the throttle body, oil was then sucked in through the flame trap. The problem was repeatable just by by giving it a moderate amount of pedal. Blue smoke and almost total loss of power. As soon as I let off the gas the bellows tube would pop back to normal shape and car would drive normal with no smoke. The tube was old and had been weakened, very soft on the bottom. One day when I looked under the hood after an incident I spotted it collapsed, it had not popped back. Replacement of the bellows tube solved the problem instantly, putting in the old tube brought the problem back.

Upon initial consideration of this syndrome one might say BS because we all know vacume decreases when throttle is opened, but that is manifold vacume. There is also a separate and very slight vacume existing between the air filter and the throttle body which increases when the throttle is opened. This is due to a much increased air flow being drawn in through the filter. I suspect that a very dirty air filter combined with the weakened bellows tube would contribute to the syndrome.

Some may doubt all this but thems my thoughts and that was my experience.
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David Hunter