I have a 1987 560SL. When I first start the car the engine RPM goes to 1,000. After a brief time the RPM drops to 500. I drive around the neighbor and stop several times. The RPM drops to 500 each time I stop. However, after the car temperture reaches normal operating range the RPM goes to 1,ooo and stays there. I recently replaced the cold start valve and some vacumn tips / lines. What could cause the RPM to go to 1000 after the car warms up? Thanks for any suggestions.