Here are some potential causes:
* Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the engine control module (ECM), causing the engine to rev uncontrollably.
* Transmission Shift Linkage/Cable: A problem with the linkage or cable connecting the shifter to the transmission could be preventing the transmission from fully engaging Park.
* Throttle Body: A sticky or malfunctioning throttle body could be causing the throttle plate to stay open even when the accelerator is not pressed.
* ECM/PCM Issue: A faulty Engine Control Module (ECM) or Powertrain Control Module (PCM) could be misinterpreting signals and allowing the high RPMs.
* Vacuum Leak: A significant vacuum leak could affect idle speed and potentially contribute to erratic behavior, although it's less likely to cause this extreme of a problem.
Why no warning lights? Not all malfunctions trigger warning lights. The problem might be subtle enough to not trigger a diagnostic trouble code (DTC) that illuminates a warning light.
What to do:
1. Don't ignore it: Continued high RPMs while in Park can damage the engine.
2. Get it checked ASAP: Take your vehicle to a qualified mechanic or auto repair shop. They can diagnose the problem using a scan tool to check for trouble codes and perform a thorough inspection.
3. Mention the specific symptoms: Be clear about the engine revving to 4500-5000 RPM *only* while in Park and that it drives normally otherwise. This helps the mechanic focus their diagnosis.
It's crucial to have this issue addressed promptly to prevent potential engine damage. The high RPMs put excessive stress on engine components.
