Well if it revs high at idle then your IAC valve might be bad. If it rev too high when accelerating then the throttle position sensor may be going bad or need adjusted.
You should check the transmission fluid. Usually that is the source of the problem for a vehicle that is revving high. When it becomes low or old, it just doesn't work as well and needs to be replaced so all the engine parts can function properly.
Start with the basics, then get more detailed. Check the engine oil, transmission fluid, battery connections, throttle body, air filter, EGR valve, fuel pump, control module, and crank shaft sensor.
