1992 Galant GTI idling problem

Hi to all,can you help me guys fix my car?I have a problem with my 1992 galant GTI DOHC engine.Everytime I start it the rpms shoots to 2000,then after a few seconds it goes back 1000.After that it goes up down playing from 2000 and 1000 for over a minute or two.Can you pleeeease help me guys fix this problem.THaNK You!!!!!