What Causes Unstable Idle and Shaking After Starting the Car?

[VanKhloe]

After starting the car, the reasons for unstable idle include engine control logic errors and air conditioning control circuit faults. Details are as follows: Engine Control Logic Error: Unable to receive the signal indicating the air conditioning is turned on. When it cannot determine whether the air conditioning is on, the engine control unit (ECU) mistakenly interprets this as a temporary high load and attempts to compensate by increasing the engine speed to offset the idle resistance. When the engine speed drops, it cannot handle the load from the air conditioning compressor, leading to another increase in speed. This back-and-forth adjustment results in unstable idle. Air Conditioning Control Circuit Error: Unable to send the air conditioning activation signal. Similar to the first scenario, because the ECU cannot determine the air conditioning status, it continuously adjusts the idle speed, leading to unstable idle performance.