Possible reasons for a drop in engine speed when braking on vehicles with an automatic transmission:
1. Engine control problems:
*Faulty throttle position sensor
* Problems with the fuel injection system
* Engine control module (ECM) malfunction
2. Problems with automatic transmission:
* Faulty torque converter (GDT)
* Slipping of friction discs
*Low or contaminated transmission fluid
* Faulty input/output shaft speed sensor
3. Problems with the brake system:
* Sticky brake calipers
* Air in the brake system
*Low brake fluid level
4. Other reasons:
* Vehicle speed sensor malfunction
* Faulty crankshaft position sensor
What to do:
1. Check the brake fluid level and add it if necessary.
2. Check the brake system for problems such as sticking calipers.
3. Check the level and condition of the transmission fluid in the automatic transmission. Replace fluid if necessary.
4. Check the engine management system using a fault diagnosis scanner.
5. Contact a qualified mechanic for further diagnosis and repair, especially if the above checks do not resolve the problem.