Why has the idle speed of the car increased?
3 Answers
The increase in idle speed of a car may be due to a dirty or faulty throttle, which causes abnormal idle speed. Other reasons for the increase in idle speed of a car: Malfunction of the idle control valve. Normally, electronic fuel injection engines determine the normal idle speed of the car through the idle control valve. During driving, the electronic control unit calculates based on the information transmitted by the car engine to adjust the intake air volume and change the idle speed of the engine. However, if oil stains or carbon deposits affect the idle control valve, the electronic control unit cannot receive accurate information, thereby affecting the adjustment of idle speed. In this case, the idle speed will become too high. Solutions for the increase in idle speed of a car: Adjust or replace the throttle position sensor; clean or replace the idle control valve and use a special decoder to perform basic settings for the idle speed; find the leakage point, reseal or replace related components; check the timing marks and readjust the valve timing according to standards; clean and check the fuel injection volume of each injector to ensure there is no blockage or leakage; replace the three-way catalytic converter; remove carbon deposits on the EGR valve or replace the EGR valve.
Last time my car's idle speed suddenly increased, which really confused me. An experienced driver told me it might be due to a dirty throttle body - when the throttle response lags, it can cause unstable idling. It could also be a problem with the mass airflow sensor; if it misreads the intake air volume, the ECU will inject more fuel. Another common issue is a faulty coolant temperature sensor - if it sends false low-temperature signals, the engine control unit will automatically increase RPM to warm up the engine. The most troublesome case is vacuum hose leakage; my old Lavida had this problem, making the idle speed fluctuate like a roller coaster. It's recommended to first read the trouble codes. If you want to DIY, you can try cleaning the throttle body. If that doesn't work, you'll need to take it to a professional shop to check the sensors and hoses.
With over a decade of experience in car repair, I've encountered numerous idle speed anomalies. The most common issue is carbon buildup in the electronic throttle body, causing the throttle plate to stick and resulting in inaccurate opening. Next is air leakage in the intake system, where unmetered air enters the engine directly, leading to a lean air-fuel mixture and forcing the idle speed to rise. Another scenario is the ECU compensating for other faults, such as a stuck AC compressor or abnormal alternator load. I recall a Corolla with an idle speed of 1200 RPM, which turned out to be a ruptured diaphragm in the crankcase ventilation valve, allowing oil vapor to leak into the intake manifold. It's advisable to first check for visible external air leaks, focusing on cracks in the intake pipes and vacuum hoses.
