Why does your 2000 Cadillac Deville DTS idle high when you turn it on?

A high idle in a 2000 Cadillac Deville DTS when first starting can be caused by several factors, including a malfunctioning idle air control valve (IAC), a vacuum leak, or a dirty throttle body. The engine management system may also increase idle speed to warm up the engine quickly or compensate for a cold start. If the high idle persists after the engine warms up, it’s advisable to have the vehicle checked for diagnostic trouble codes and to inspect the related components for any issues.