Possible reasons for floating engine speed when engaging reverse gear on an automatic transmission:
1. Low transmission oil level:
* Insufficient fluid level leads to loss of pressure and clutch slippage, which can cause speed fluctuations.
2. Worn or dirty clutches:
* Worn or dirty clutches can reduce their ability to transmit torque, resulting in slippage and unstable rpm.
3. Problems with the automatic transmission valve body:
* A faulty or dirty control valve can affect transmission fluid pressure, causing RPM fluctuations.
4. Worn torque converter:
* The torque converter liquefies torque from the engine to the transmission. A worn or damaged torque converter can interfere with power delivery and cause RPM fluctuations.
5. Electrical faults:
* Faulty sensors or electrical connections can affect the operation of the automatic transmission, including engine speed control.
6. Malfunction of the automatic transmission control module (TCM):
* TCM controls the operation of the automatic transmission. A faulty TCM may not properly control fluid pressure or engine speed, causing the RPM to float.
Solution:
* Check the transmission oil level and add it if necessary.
* Have a mechanic diagnose and replace worn or damaged clutches, valve body, torque converter or other faulty components.
* Correct any electrical problems by replacing faulty sensors or connections.
* Scan trouble codes using a diagnostic scanner to determine if there is a TCM malfunction. If the TCM is faulty, it may need to be replaced.