IAC(idle air control) valve would be a good place to start
On upper intake/throttle body, 2 wires connected
Computer opens it all the way for starting, all fuel injected engines use some form of IAC Valve, and all will REV high on startup, but then should drop to "target" idle, 1,200cold, 750 warmed up are targets
Unbolt IAC from intake, then plug its wires in, if you took then off
Turn on the key
It should be open all the way, look at the valve inside
Now unplug the 2 wires and it should close all the way
Plug wires in again, and it should open all the way
Repeat until you are satisfied it is not sticking open
It is just a 12volt solenoid, key on engine off gives it full 12volt
After engine starts computer varies the voltage to close it a bit to set "target" idle RPMs