The IAC (idle air control) at the throttle body is usually the problem.
Sounds like the Idle Air Control valve.
Answernot enuff info in question does it do this when a/c is being used a/c cycles on and off to maintain temp setting engine will idle up to run a/c the down again whe a/c cycles offno you start it and it stays at high idle
water pump or thertomstat
The Idle Air Control (IAC) valve is mounted on the throttle body
ford suck. go Chevy
Vacume hose(s)/system problem, or dirty fuel filter would be my first 2 guesses.
A good chance its the Idle Control Valve
It sounds like you have a vacuum leak from either a vacuum hose or a leak or crack in your intake. Check for hissing sounds.
There is no adjustment you should mess with. The ECM maintains the correct idle unless you have problems like vacuum leaks.
Throttle plate may be stuck - try to free with a screwdriver
There should be a screw near the end of the throttle cable on the throttle body.
idle speed controll or tps throttle sensor