* Transmission Issues: This is the most probable cause. A problem within the automatic transmission (if equipped) is preventing it from smoothly transferring power to the wheels. This could include:
* Low transmission fluid: Check the fluid level and condition. Low fluid or burned fluid indicates a serious problem.
* Failing torque converter: The torque converter may not be locking up properly, leading to slippage and a lack of power transfer.
* Internal transmission problems: Worn clutches, bands, or other internal components can cause similar symptoms. A professional inspection is necessary.
* Problems with the shift solenoids or other transmission electronic components if it's an electronically controlled transmission.
* Clutch Problems (Manual Transmission): If it's a manual transmission, the clutch could be slipping, worn, or improperly adjusted. This prevents efficient power transfer when engaging a gear.
* Weak or Failing Components in the Drive Train: Problems with the drive shaft, differential, axles, or wheel bearings could lead to a similar issue. This is less likely, but worth considering if the transmission checks out.
* Fuel Delivery Under Load: While less likely given the smooth idle and revving, there's a slim chance the fuel pump is struggling to keep up with the increased demand when under load. This is more likely to manifest as hesitation or a lack of power rather than a direct stall, though.
* Ignition System Problems Under Load: A failing coil pack, ignition wires, or distributor cap (if applicable) might function fine at idle but falter under the increased electrical demand when the engine is under load. Again, this is less probable than the transmission issues.
Troubleshooting Steps:
1. Check Transmission Fluid: This is the absolute first step. Low or dirty fluid is a significant indicator of a transmission problem.
2. Listen for unusual noises: When putting the car in gear, listen carefully for grinding, whining, or other unusual sounds from the transmission area.
3. Test Drive (carefully!): If you can safely do so, try driving very slowly and gently, paying close attention to how the car responds. Does it stall immediately or after a short delay?
4. Professional Inspection: Given the symptoms, a professional mechanic specializing in transmissions is needed to diagnose and repair the issue. Trying to troubleshoot these problems yourself without the proper tools and knowledge can be risky and costly.
Do *not* continue driving the car extensively if it stalls when put into gear. You risk causing further damage to the transmission.
