What causes fast idle on 1998 Mercury Tracer?

Fast idle on a 1998 Mercury Tracer can be caused by several factors, including a malfunctioning idle air control (IAC) valve, which regulates the engine's idle speed. A vacuum leak in the intake system can also lead to higher idle speeds by allowing extra air to enter the engine. Additionally, issues with the throttle position sensor or a dirty throttle body may contribute to erratic idle behavior. Proper diagnostic testing is essential to pinpoint the exact cause.