I crank up the engine initially to start, the idle doesn't steady itself

I have a 98 Toyota Camry LE, V6 engine. I just made it over 140K miles. Recently this has been happening, when I crank up the engine initially to start, the idle doesnt steady itself (when it is supposed to, like to heat it up) instead it just dies down. So what i've been doing is if its a 1st start, I press on the gas pedal and hold on down for 5 mins or so, until I feel the engine like rev up (thats how I know it has idle already). But why is this? Whats wrong with the engine, is it a TUNE-UP that I need?