Add a second, temporary, return spring on the throttle linkage, this will test if it is a throttle plate problem.
If so equipped, disconnect Cruise Control cable from throttle linkage, the cable is pulled by a vacuum actuator, if it is leaking it may cause increased engine speed.
TPS(throttle position sensor), this tells the computer what the driver wants to do, accelerate or decelerate, it is a simple variable resistor, like a Light Dimmer or Volume Control.
Top wire on the TPS will have 5 volts coming from the computer
Center wire is the voltage sent back to the computer telling it what the driver wants.
.69-.99 volts is on the center wire when throttle is closed all the way
Above 4.6volts is on that wire when throttle is Wide Open
Bottom wire is Ground.
If you turn on the key and put a sewing pin in the center wire, you can test the voltage.
Set Volt Meter to DC Volts
As you open the the throttle voltage on center wire should increase steadily no jumping around, same when you close throttle.
Any odd voltage jumps will be read by the computer as add more or less gas, so swap it out if you see and jumping volts.
IAC(idle air control) valve, the sets the idle on fuel injected engines, it isn't a Ford thing all fuel injected engine use this, it is an air by-pass on the throttle body, like a controlled vacuum leak.
The computer controls this Valve, when you first start a cold engine RPMs go up to 1,500+ then drop back down to about 1,100, as engine warms up RPMs drop to 650-750, that's all done using the IAC valve.
So it can let enough air in to accelerate the vehicle if there is a problem with it.
And then there is a possibility of a vacuum leak, PCV hoses are often a common leak point which can come and go.
After engine warms up let it idle, move around some of the vacuum lines, see if you get an increase in the idle.
Unplug wires in IAC valve, RPMs should drop to 500 or engine may even stall either is OK if means no vacuum leak.