What does unstable vehicle idle speed mean?
2 Answers
Unstable vehicle idle speed refers to the situation where, after the vehicle is started and in neutral stationary state, the engine speed fluctuates up and down. Severe instability may lead to engine stalling. The causes of unstable vehicle idle speed include: 1. Improper air-fuel mixture ratio in the engine compartment; 2. Prolonged use of spark plugs causing aging of ignition coils, high-voltage wire aging, and leakage issues that reduce ignition capability; 3. Carbon buildup on engine valves and intake ports, where carbon deposits absorb fuel and reduce vehicle power; 4. Malfunctioning coolant temperature sensor. Solutions for unstable vehicle idle speed include: 1. Replacing spark plugs; 2. Cleaning valves and intake ports; 3. Checking the coolant temperature sensor.
I've been a seasoned driver for over 30 years. Unstable idle refers to when the engine speed fluctuates up and down while the car is stationary, with the tachometer needle constantly jumping around, causing the vehicle to shake violently. I've personally experienced this - once at a red light, my car suddenly shook like a massage chair. Upon careful inspection, I found it was caused by aged spark plugs leading to inconsistent ignition, and incidentally discovered severe carbon buildup in the throttle body blocking airflow. This issue isn't just uncomfortable, it can even cause stalling on the road, which is dangerous. If left unresolved for too long, it accelerates engine wear and dramatically increases fuel consumption. I recommend going to a repair shop early for computer diagnostics, cleaning the intake tract, or replacing the air filter. For daily maintenance, avoid prolonged idling and regular highway driving helps reduce carbon buildup.
