What to Do If the Car Idle Speed Is Constantly High?
2 Answers
There are several main reasons for a car's idle speed being constantly high: 1. Idle control valve failure: The normal idle speed of an electronic fuel injection engine is determined by the idle control valve. The electronic control unit calculates signals such as engine speed, temperature, throttle switch, and air conditioning switch, then adjusts the idle control valve to open the intake bypass channel or directly increase the throttle opening to increase the intake air volume, thereby raising the engine idle speed. Solution: Check the action sound of the idle control valve. If there is no sound, it indicates a fault in the idle control valve. 2. Intake system leakage: Normally, the intake air volume must be strictly limited. If there is a leak in the intake pipe, the air flow sensor cannot measure the actual intake air volume, causing the electronic control unit to inaccurately control the intake air volume, resulting in unstable idle speed. Solution: Locate the leak and reseal or replace the relevant components. 3. Fuel injector dripping or clogging: If the fuel injector drips or clogs, it cannot inject fuel as instructed by the electronic control unit, leading to an overly rich or lean mixture, causing poor performance in individual cylinders and unstable idle speed. Solution: Measure the fuel injection volume of the injector. If the injection volume exceeds the standard, the fuel injector is dripping.
When my car has high idle speed, I start by checking around the engine first. Throttle valve carbon buildup is a common cause—frequent city traffic leads to oil and dirt accumulation, causing inaccurate throttle opening and resulting in increased idle speed. I usually remove the air filter box and spray cleaner inside, then wipe it down. If the problem persists after cleaning, I need to check whether the idle control valve is stuck or damaged. Faulty signals from sensors like the oxygen sensor can also often cause issues. If the ECU control is malfunctioning, disconnecting the negative battery terminal for a few minutes and restarting might help. Vacuum hose leaks are trickier—each hose connection needs to be inspected for cracks or looseness. Ignoring high idle speed can lead to a sharp increase in fuel consumption and even engine overheating damage. So, I recommend addressing it early. If DIY solutions don’t work, take it to a professional repair shop for diagnosis to prevent small issues from escalating. Regular maintenance, including cleaning related components, can prevent problems in advance.
