Chevrolet Repair: Tahoe over acelerated, chevy tahoe, cold start

Question
Good afternoon , I have a  Chevy Tahoe, 4x4, 1996,Motor Vortex ,gasoline, automatic ,  milleage: 192000 miles.
The problem is on the started of the motor. When I turn the key the motor reach 1400 RPM , the motor remains accelerated for 3-5 sec to reached 1900 rpm ( without press the gas pedale), after that the r.p.m. goes down until 600-700 rpm in parking drive and then the motor work in good conditions, if  I drive the truck some miles, it work OK , the problem is only when the motor is started . I have the same problem each time I started the motor.
Five months ago I had the same problem but suddenly dissapeared.  

Answer
the raise on rpm is expected, and supposed to happen. its called a cold start. when you first start it, its supposed to go up in rpm then down after a few seconds. i have a 2003 trailblazer, and it does the exact same thing in the mornings, or whenever the truck sits for a little. all cars do. the computer tells the throttle body to close off air for a few seconds, then it opens it up to where its supposed to be. thats where you get the 600-700 rpm.