Get your IACV cleaned. It is connected to the intake mainfold, and just to the right of the main block, and is silvery metal so you'll be able to identify it easily.
I had the EXACT same problem as you. Got my IACV cleaned today, which was filled with "kachra" (rubbish). As soon as it cleaned and reconnected, the car started easily and smoothly without any RPM problems. I even start my car on AC with fan speed 4, and the RPMs stay stable. So go for it as soon as possible.
I paid 500 for whole computerised cleaning + cleaning the IACV. Alone, it should cost between 250-300 and take about 45 mins.