Possible reasons:
* Throttle Position Sensor (TPS) problems: The TPS tells the engine ECU about the throttle position. A faulty TPS may incorrectly indicate throttle position, causing idle speed to fluctuate.
* Faulty Coolant Temperature (ECT) sensor: ECT tells the engine ECU about the engine temperature. A faulty ECT can result in improper fuel and idle speed control.
* Idle Air Control (IAC) problems: The IAC controls air flow at idle. A faulty IAC can cause an unstable idle speed.
* Dirty throttle body: Deposits and dirt on the throttle body can prevent it from moving smoothly and cause RPM fluctuations.
* Faulty Engine ECU: The engine ECU controls engine operation, including idle speed control. A faulty ECU can cause unstable rpm.
*Wiring or connection problems: Faulty wires or connections can disrupt communication between the sensors and the ECU, resulting in idle speed problems.
*Transmission slipping: The transmission may slip at low speeds, causing RPM fluctuations.
Diagnostics and repair:
1. Connect the scanner to the vehicle’s diagnostic port to read trouble codes.
2. Check TPS, ECT and IAC sensors to specifications.
3. Clean the throttle body and check for damage or contamination.
4. Check the operation of the idle air control.
5. Check the wiring and connections between the sensors and the ECU for faults.
6. If the engine ECU is faulty, it needs to be replaced.
7. If the transmission slips, it should be repaired or replaced.