I agree with ARI ONE my sons 93 legend was having problems with the heat system the same as you and when I tore the motor down I found a crack in the head gasket, but I bought a re man motor and replaced it,it cured the reving problem and the wierd overheating problem, as far as the speedo and 4th gear indicator flashing it will be the vss,already been there and replaced that,and as far as your stereo goes in your service manual their as a card which will give you disabler code to re set your stereo. Im a retired mechanic.