Arne, There are several things which can control idle speed on start up. The 1st thing I would do is check out or replace the Idle speed thermister. This is what senses the temp of the water and changes resistance that the idle speed ECU reads and then adjust the motor. The idle switch has to be adjusted properly also to power the ECU or nothing will happen. Make sure you have no vacuum leaks on the tube going into the the lower part of the intake manifold. Since the idle does come down, this would be my first thing to check. There are other compoents that will effect idle, but it would be more to do with staying high or low all the time. Example, open or shorted diode, Vacuum, Throttle plates not closing, or bad Idle motor. or even a bad Idle ECU. John Hervey www.specialTauto.com