Electrical problem
1999 Suzuki Baleno 4 cyl Two Wheel Drive Automatic

Hello to you all
Problem:

Run the car at the beginning of the morning or a cold
Van Meter of the RPM down more than usual about
100-150 rpm and then noticed that
An auto engine down, and continue to do so
For 2 seconds and then begin to rise as the rpm
He enjoined should also be made.

Question if I may:

Is the problem the engine temperature sensor ?

Is The problem The Idle valve ?

Or that there is another problem?

Note:
Been cleaned up thethrottel , but to no avail.

With thanks to you all.