Hi there, I've no direct experience working with the aerial on the MR2.
However... I do know one thing, if the headunit is aftermarket and it is not connected to a live/earth correctly, the aerial will refuse to budge up or down.
This happened to me a few weeks back, the aerial in this case was working, but its motor had no power from the headunit to rise up out of the body.
My solution was to splice a live correctly on the ISO harness and hey presto.
Is your headunit/radio factory or aftermarket?