Problem is the engine revs up and down on its own

If you hit the Rev Limiter on a Ford, it will simply bounce the rev back down, to protect the Engine. So, no high Revs. But, you should be able to bring it slowly to a High RPM. That is normal. If there are no Check Engine Light on. You are most likely hitting the rev Limit and need to stop.

Could be a crankshaft sensor.

How is it at idle? A fast idle might be the result of a vacuum leak. Is there a check engine light with a code? Did you clean the mass air flow sensor?

have the OBD read by a suitable mechanic ,sounds like an engine sensor ,the crank sensor would be my first thought as the rev, info is sent from that sensor but you need the code to be sure

If the engine has a constant miss the computer should record a trouble code or two.
Is the check engine light on ?

engine Normally revs up upon start up of car.Then goes down after a few minutes.If not, then adjust the timing of iac and TPS.

Engine revs on its own, like? it revs up & down, up & down, if so, it is your Idle Air Control Valve (IAC Valve)

it has a rev limitor on it.. at high revs the computer shuts the engine down to prevent damage.

you need to clean or replace your idle air control valve(IAC). The IAC allows your engine to idle smoothly by opening and closing a valve that allows air flow to the engine that is monitored by the computer. The IAC get dirty causing it to stick and move slower than it should which causes the up and down idle

clogged intake manifold