What is the fault of unstable engine idle speed?
2 Answers
Engine idle instability refers to the variation in gas forces within the cylinders, causing an imbalance in power output among cylinders. This results in inconsistent horizontal forces on the pistons during the power stroke, creating an unbalanced torque that tilts the engine laterally, leading to engine vibration. The causes of unstable engine idle speed include: 1. Excessive carbon buildup in the throttle body and air flow meter; 2. Heavy carbon deposits on pistons in the cylinder combustion chamber; 3. Weak spark due to faulty spark plugs; 4. Fuel pressure issues; 5. Intake manifold or various valve leaks, fuel pressure faults, low oil pressure, ignition system failures, etc., can all contribute to unstable engine idle.
This issue can be minor or serious. Last time I encountered fluctuating idle speed, it was due to a dirty throttle body. Cleaning the throttle body can solve many problems. It could also be caused by excessive carbon deposits or clogged fuel injectors. Worn-out spark plugs can make the engine struggle, especially with noticeable shaking during cold starts. A dirty air filter restricting airflow can also cause shaking. If you notice the steering wheel shaking along with it, check if the engine mounts are aged or cracked. The easiest way is to connect a diagnostic scanner to read the fault codes—within three minutes, you’ll know if it's the ignition coil or oxygen sensor acting up. For older cars, remember to use fuel additives regularly to clean carbon deposits and avoid filling up at unreliable gas stations to save money.
