1993 Grand Am high RPM

My 1993 pontiac gand am (3.4L) goes into high rev.
3000 rpm aprox. At will, ether well driving or upon start up as well the check engine comes on only when this happens. My machanic put it on his scope and got every code come up, he said try changing the computer but was unsure if this would solve it. With 165000KM on it the car runs great other than this problem, any suggestions will be greatly appreciated.

thanks
Greg