In my Cultus, RPM behaves normal at cold start. And behaves normal even if I keep the engine running for hours at idle.
But if I drive my car for a while, then stop, press clutch or slow down my car, the RPM starts to drop. And issue is even worse with Headlight, AC, or Both turned on.
That's why in workshops, after the Mechanics/Electricians fix the RPMs, it behaves normal while testing but it's a temporary fix. The issue reappears after driving for 20-30 Minutes.