I don't know specifically what would be causing it, but I'll speak of a similar problem on my truck and what it turned out to be.

I'm sure you of all people are familiar with the fuel heater plate in the manifold below the carburetor on 22Rs. It also goes through the coolant bypass passage on the underside of the manifold. What had happened was when the dealer replaced that gasket, they just used a slop 'o' RTV instead of a gasket, and it had degraded to the point where under hard acceleration, it was sucking coolant through in quantities just large enough to make the truck smoke like it had a bad head gasket.

I'd look for things that intersect the intake manifold that contain something other than air... coolant, EGR, PCV, oil, anything that might be sucking in under those sorts of situations.

It's a place to start anyway. <img src="/forums/images/graemlins/confused.gif" alt="" />