The past few days when I start my car,
the engine would idle at around 1100 to 1200.

After driving it for a couple of minutes,
it would go back to the 800-900 idle rpm.

Anyone know what the dilio?

 

Mine's always done that when the engine's cold - the computer is programmed for a "high idle" (around 1100 RPM), and then drops down to 780 after the engine's begun to warm up.

It serves the same purpose as the choke or fast-idle circuit in a carburetor - to make it easier for the engine to stay running until it's warmed up.

 

If the A/C is on it will also raise the idle a little bit as well...