Possible reasons for the drop in speed when turning on the automatic transmission in a Mercedes:
1. Throttle Position Sensor (TPS):
* Incorrect TPS readings may cause the engine to not receive enough fuel when shifting into gear.
2. Idle Air Control (IAC):
* IAC controls idle speed. Its malfunction can lead to a drop in speed when the gear is engaged.
3. Engine Control Module (ECM):
* The ECM monitors various engine and transmission components. A malfunctioning ECM can result in improper engine speed control.
4. Transmission problems:
* A problem with the transmission, such as worn clutches or a faulty hydraulic control unit, can cause the RPM to drop when shifting gears.
5. Insufficient fuel pressure:
* Insufficient fuel pressure can lead to a lean air-fuel mixture and a drop in speed.
6. Electrical wiring fault:
* An open or shorted circuit in the wiring connecting the engine sensors to the ECM may result in improper engine speed control.
7. Air intake problems:
* Air leaks in the intake system can allow additional air to enter the engine, which can lead to a lean air-fuel mixture and a drop in rpm.
8. Malfunction of the mass air flow (MAF) sensor:
* MAF measures the amount of air entering the engine. Incorrect MAF readings can cause the engine to not receive enough fuel.
How to fix the problem:
*Check TPS using a diagnostic scan tool.
* Check the IAC for blockage or malfunction.
* Read trouble codes using a diagnostic scanner to determine possible ECM problems.
* Check the transmission fluid for leaks or overheating.
* Check the fuel pressure at the fuel rail.
* Check wiring for breaks or shorts.
* Inspect the air intake for leaks.
*Check the MAF using a diagnostic scan tool.