Please help

 

Fuel injected engines have no "jets" like a carb so an "idle screw" won't work very well.

And fuel injected engines need a computer to time the injector pulses so same computer was also used to control the idle.
It does this using the IAC(idle air control) valve, this valve is opened and closed by an electric motor controlled by the computer.
It is in essence a controlled vacuum leak, more air in = high idle, less air = lower idle

At start up engine RPMs should surge to 1,500+ rpms, computer opens IAC valve all the way to test it, this is normal.
Then idle should drop to "target RPM", cold engine RPM is based on temperature, usually around 1,100rpm.
Warm engine RPM will be 700-800, depending on manual trans or automatic trans.
If idle never surges at startup or changes when engine is warm or cold then IAC Valve may be bad.

If you unplug the IAC valve wires with warmed up engine, the RPMs should drop to 500 or engine may even stall, either is correct, if RPMs don't drop that low then you have a vacuum leak somewhere, leave IAC valve unplugged and try to find the leak.


If RPMs do drop to 500 or lower then computer was setting high RPMs for some reason, I would check for Codes via OBD 2 reader