I have a 92 prelude and when i start it up the car rumbles as if it was going to stall out?

and i have to give it gas for about 5-10 seconds around 2000 rpms before it idle's normally. Funny thing is after the first 5-10 of it doing this weird rumbling or what ever its doing it runs fine, the idle returns to normal and runs smooth while im driving it. Unfortunately i have to go through this every time i go to start the car. what is the problem?