What causes the engine yellow light, difficulty starting, and low idle speed?

[MasonRose]

Engine yellow light, difficulty starting, and low idle speed may be caused by oxygen sensor failure or spark plug carbon buildup. Below is a detailed explanation of the possible causes: Explanation of oxygen sensor failure: Modern vehicles are equipped with two oxygen sensors, one before and one after the three-way catalytic converter. The front oxygen sensor detects the air-fuel ratio under different engine operating conditions, while the ECU uses this signal to adjust fuel injection and calculate ignition timing. Explanation of spark plug carbon buildup: Poor-quality fuel and congested urban traffic make it easy for spark plugs to accumulate carbon deposits. Spark plug carbon buildup can lead to poor engine performance, resulting in symptoms such as difficulty starting, unstable idle speed, poor acceleration, backfiring during rapid acceleration, excessive exhaust emissions, and increased fuel consumption.