What Causes a Sudden Increase in Engine Idle Speed?
3 Answers
An excessively high idle speed in a car is primarily caused by too much air intake during idling, excessive fuel injection, or incorrect engine control signals. Below is an introduction to car idling: 1. The function of car idling: Idling is a working condition of a car, referring to the engine running in neutral. The engine speed during idling is called the idle speed. The idle speed can be adjusted by changing the throttle size, among other methods. Idling means the engine is 'producing power without doing work.' When the engine is running, if the accelerator pedal is completely released, the engine is in an idle state. 2. Reasons for unstable idle speed: Direct causes refer to mechanical parts being dirty, worn, or incorrectly installed, leading to changes in cylinder power, resulting in an imbalance of power among cylinders and causing unstable engine idle speed. Indirect causes refer to abnormalities in the engine's electronic control system, leading to poor combustion of the air-fuel mixture, making it difficult to balance the power among cylinders and causing unstable engine idle speed.
Last week while waiting at a red light, my car's engine RPM suddenly surged to over 2000, making a loud buzzing noise that gave me quite a scare. After checking, it might be due to dirt stuck in the throttle body preventing it from closing properly, or an air intake leak allowing excess air to disrupt the air-fuel mixture. Other possibilities include a faulty idle control valve or loose wiring harness, which could cause the ECU control system to frantically increase RPM to prevent stalling. This issue has significant impacts: fuel consumption can instantly spike by 1-2 points, and braking feels unstable, greatly reducing safety. It's crucial to immediately stop and inspect the air filter and sensor connections. If you can't fix it yourself, head to a 4S shop or repair shop promptly to prevent the problem from worsening and costing more.
I've been into car modifications for over a decade, and I can usually tell what's wrong when the idle speed abnormally increases. The most common causes are cracked vacuum hoses or aged leaking connectors, which allow unfiltered air into the engine and disrupt the ECU's air-fuel ratio calculations. It could also be carbon buildup on the throttle body causing it to stick, making the opening uncontrollable, or a stuck idle control valve that can't automatically adjust the speed. These issues often stem from inadequate routine maintenance, like not cleaning the engine bay regularly or using low-quality fuel. Deeper causes include sensor failures, such as the intake air temperature sensor sending false low-temperature signals, prompting the ECU to raise the idle speed for 'warming up.' If you're handy, you might inspect the parts yourself, but for safety, it's better to leave it to professional mechanics to avoid causing more problems.
