recently when i start my car, the engine idle speed is very low,
> under 700rpm, but after a few minutes it will come back
Search Google Groups - Camry for "IAC." Idle air control valve. One 10mm bolt at the clamp near the throttle body to remove the air intake hose, then spray emissions control safe carburetor cleaner into the small rectangular hole right in front of the throttle body, on the bottom, while using your other hand to move the throttle valve to keep the engine running. By spraying cleaner through the valve, should free up its operation. Because the PCV valve vents in this area, can cause the IAC to stick sometimes on start up. This is assuming you have the 4 cylinder. Six cylinder may be different.