RPM

I have a Toyota Camry 4 dr sedan 4 cyl. Mileage is 140,000.
I have a problem usually in the morning.
whenever I start my car RPM goes down until it engine dies out.
I have to step firmly on gas pedal for a while before(maybe 2-3 mins.) With high RPM before it goes normal.
OR
after I switch the key on, I step on the gas pedal three times then start the engine and wait until the RPM is high enough to maintain the normal idle of my car.

BUT during the day, once I start the engine on, there are no problems with the RPM(idling).

hope somebody can enlighten me on this problem.
thanks.