Answers:
1) ECU will always try to control the RPM's at 775 AT IDLE which means your foot is off the gas and the idle speed microswitch is depressed. It can't do this if the curb idle screw is not set correctly or there is some other vacuum leak, decel springs , etc.
2) ECU controls idle speed only at idle. It does nothing when your foot is on the gas.
3) Yes
If your idle microswitch is flakey, you have a bad wiring connection, or the screw is barely touching the switch, and the switch fails to close AT IDLE, the RPMS will go up to 1,300 or so.
The decel springs are in the throttle body, you can see them if you remove the W pipe from the front of the intake manifold. You can clean them with carb cleaner but they are almost certainly "OK" as long as the look like a coil and evenly spaced / not collapsed.