Unstable idle in Ford Mondeo

I have a 1.8 16v gasoline mondeo of the year 2001 and the idle when I stop in a semaphor rises to 1400 Rev and then download to 900 rev some manual where you can see what can be the cause of mismatch, thank you

Check the tps the Ford usually fails.

IAC valve

Thank you for answering both but I don't know what the TPS is or where the IAC valve is, if you could explain a little more I appreciate it.

The TPS is the positioning sensor of the acceleration butterfly, and it is located in the switching body, it has the form of a snail the plug is above just disconnect it and try the truck like this, the IAC is, the IAC is the relief control valve and it is placed in the same body but opposite Membrane and works both high and low, but it is easy to check if you disconnect it the engine should accelerate a lot or turn off, if it is the same is bad, or you hit it on top and if it varies the revolutions it is in poor condition,