* Torque Converter Issues: The torque converter is the fluid coupling between the engine and transmission. If it's failing (worn clutches, internal damage), it might not be able to handle the load of the engine when put into gear. The engine might stall because it can't overcome the resistance.
* Transmission Problems: A failing transmission could be the source. Low transmission fluid, worn internal parts, or a problem with the valve body could all cause the engine to stall under load. This is especially likely if there are also other transmission issues like slipping gears or hard shifting.
* Low Transmission Fluid: This is a crucial check. Low fluid leads to inadequate lubrication and pressure, impacting the torque converter and other transmission components.
* Vacuum Leaks: The transmission's operation often relies on vacuum assist. Leaks in vacuum lines can affect shifting and cause stalling.
* Engine Problems (Less Likely): While less likely given the symptom, a weak engine, especially one with ignition, fuel delivery, or compression issues, might only be able to maintain idle speed, but not generate enough power under load when the transmission engages.
* Computer/Sensor Issues (Possible): The car's computer system controls various aspects of the engine and transmission. Faulty sensors (like a speed sensor) or a failing computer could send incorrect information, leading to the stalling.
Troubleshooting Steps (in order of priority and ease):
1. Check the Transmission Fluid: This is the first thing to do. Low or dirty fluid is a common cause. Check the fluid level (with the engine running and warmed up), and note its color and condition.
2. Inspect Vacuum Lines: Look for any cracked, loose, or disconnected vacuum lines related to the transmission.
3. Listen for Unusual Noises: When the car is running in Park, listen carefully for any unusual noises coming from the transmission. Whining, grinding, or banging could indicate internal problems.
4. Test the Torque Converter (Advanced): This is more difficult and may require professional help, but it involves assessing the torque converter's ability to lock up.
5. Professional Diagnosis: If the problem persists after the above steps, take the car to a mechanic specializing in older cars or transmissions. They'll have the tools and experience to diagnose the issue accurately. A proper scan of the car's computer system could reveal error codes related to the transmission or other systems.
Don't attempt extensive repairs yourself unless you have significant mechanical experience, as improper repairs can worsen the problem. The problem is likely in the drivetrain and not something easily fixed by an amateur mechanic.
