cruise control continues to accellerate

[fast-e-nuff!!]

I have a 1994 850 base wagon non turbo. When I turn on and set the cruise control it does not stay at the set speed, it simply continues to accellerate. When I hit the brakes it disengages normally but when I hit resume it does the same thing, continues to accellerate until I brake or turn it off. Even pushing the decelerate side of the button only results in uncontrolled accelleration. Any ideas? Great site thanks a lot, I've learned a bunch already!!