Here are some more likely culprits:
* Throttle Cable or Electronic Throttle Control (ETC) System Malfunction: A sticking or damaged throttle cable (if your car has a cable-operated throttle) or a problem with the ETC system (more likely in a 1999 car) could cause the throttle to remain open, leading to unintended acceleration. This is a prime suspect given your description. A faulty sensor or actuator within the ETC system could be sending incorrect signals to the engine control module (ECM).
* Transmission Problems: Issues within the automatic transmission, such as a malfunctioning valve body or a problem with the shift linkage, could cause the transmission to remain in a lower gear or not disengage properly, resulting in unintended acceleration.
* Vacuum Leaks: A significant vacuum leak in the intake system could affect the engine's operation and potentially lead to erratic behavior, including unintended acceleration.
* Engine Control Module (ECM) Failure: The ECM controls many aspects of the engine's operation. A malfunctioning ECM could send incorrect signals to various components, potentially causing unintended acceleration.
* Faulty Speed Sensor: While less likely to cause the *full* problem you describe, a faulty speed sensor could provide incorrect information to the ECM leading to unpredictable behavior.
What you should NOT do:
* Continue driving the car. This is extremely dangerous.
What you SHOULD do:
* Have the car towed to a qualified mechanic immediately. Do not attempt to drive it.
* Do not attempt DIY repairs. This is beyond the scope of most home mechanics and attempting to fix it yourself could worsen the problem or lead to injury.
* Describe the problem in detail to the mechanic. Make sure they understand that the car accelerates uncontrollably and requires the engine to be shut off to stop it.
This is a serious safety hazard that needs professional attention. Ignoring the problem could result in a serious accident.
