What are the reasons for slightly high car idle speed?
4 Answers
The reasons for slightly high car idle speed are: 1. The idle switch does not close; 2. The idle control valve is faulty; 3. There is air leakage in the intake pipe; 4. Incorrect valve timing; 5. Fuel injector dripping or clogging; 6. Exhaust system blockage; 7. The EGR valve opens during idle conditions. Solutions for slightly high car idle speed: 1. Adjust or replace the throttle position sensor; 2. Clean or replace the idle control valve and use a decoder to perform basic idle speed settings; 3. Locate the leakage point, reseal or replace related components; 4. Check the timing marks and readjust the valve timing according to standards; 5. Clean and check the fuel injection quantity of each injector to ensure there is no clogging or dripping; 6. Replace the three-way catalytic converter; 7. Remove carbon deposits on the EGR valve or replace the EGR valve.
I've been running a repair shop for years, and there are many reasons for high car idle speed. The most common one is carbon buildup in the throttle body, which prevents the throttle from closing properly, causing the engine to suck in extra air. Or there could be a leak in the intake system, such as a cracked hose, where air leakage interferes with idle speed. If the idle control valve is faulty, it will mess with the RPM, and if the temperature sensor gives the wrong signal, the ECU may mistakenly think the engine is too cold and automatically increase the speed. If these issues aren't addressed, fuel consumption will skyrocket, and the engine may overheat, potentially damaging the car. It's recommended to first clean the throttle body or check the vacuum hoses to prevent small problems from turning into big troubles—saving money and being eco-friendly.
My car had a high idle speed issue, mainly due to thick dust buildup around the throttle body, especially when driving frequently in congested urban areas where carbon deposits tend to accumulate, making the idle unstable. A dirty air filter can also restrict airflow, leading to higher RPMs. This is more noticeable during cold starts—for instance, if the coolant temperature sensor fails, the ECU might think it needs to warm up the engine. Last time, I disassembled and cleaned it myself, and the idle returned to normal. High idle not only wastes fuel but also creates noise. Regular maintenance is key—don’t wait until it breaks down completely to fix it.
The engine idle speed is high, and I reckon it's mostly a minor issue with the intake system. Check if the throttle body is clogged with carbon deposits or stuck, or if there's an air leak at some point. If the sensor malfunctions, the ECU control will go haywire. These minor repairs aren't expensive, but if left unattended, they can lead to higher fuel consumption and engine damage. Have a technician test it with equipment as soon as possible, and replacing the parts should solve the problem.
