What Causes Engine Idle Fluctuation?

[DeJulianna]

Reasons for engine idle fluctuation: 1. Severe carbon buildup in the engine: Carbon deposits are the main cause of engine shaking. When excessive carbon accumulates inside the engine, the fuel injected by the cold-start injector gets largely absorbed by the deposits, resulting in an overly lean air-fuel mixture during cold starts and making cold starts more difficult. Solution: Regularly clean the fuel system, inspect the idle air control valve, and clean the throttle body. 2. Ignition system malfunction: Spark plugs are wear items that require periodic replacement. If excessive carbon buildup on spark plugs or excessive electrode gap is found, replacement is needed. Additionally, inspect the condition of ignition wires and coils. A vehicle diagnostic computer can be used to assess the ignition system's status. 3. Fuel pressure issues: Check whether fuel supply pressure and intake pressure sensors are functioning properly. Abnormal fuel pump pressure or faulty readings/operation of the intake pressure sensor can both cause engine shaking.