What Are the Causes of High Car Idle Speed?
3 Answers
The causes of high car idle speed include: 1. Throttle sticking or not closing properly; 2. Additional air valve failure; 3. Idle speed control valve failure; 4. Water temperature sensor failure; 5. Air conditioning switch or power steering pressure switch failure; 6. Crankcase forced ventilation valve failure; 7. Intake system air leakage; 8. Generator charging voltage too low. The solutions for high car idle speed are: 1. Check the operating sound of the idle speed control valve. If there is no sound, it indicates a fault in the idle speed control valve; 2. Locate the leakage point and reseal or replace the relevant components; 3. Measure the fuel injection volume of the injector. If the fuel injection volume exceeds the standard, the injector may be dripping.
I've been running an auto repair shop for over a decade, and high idle speed issues pop up all the time. The most common culprit is carbon buildup in the throttle body - when sludge gets stuck in those tiny gaps, it allows uneven air intake, making the ECU compensate by injecting more fuel. Sometimes it's a cracked intake pipe leaking air, especially when rubber hoses age and develop splits. Faulty sensors can also be to blame; a bad coolant temperature sensor might make the engine think it's still cold, causing it to rev unnecessarily when it's actually warmed up. Sticking idle control valves are another frequent offender - they get jammed halfway when they should return to position. I advise car owners to regularly clean their throttle bodies and monitor cold-start RPM fluctuations. If you notice your tachometer won't settle at stoplights, get it fixed early to save on fuel costs.
Last time my car's idle speed suddenly rose to 1500 RPM, and through my own investigation I found several possible causes. First, check if the air conditioning is properly turned off - the compressor increases load and naturally raises RPM. Then inspect the vacuum lines; loose connections causing leaks can make the RPM fluctuate. A weak battery can also confuse the ECU - a friend fixed unstable idle just by replacing the battery. Faulty spark plugs causing cylinder misfires create imbalance, indirectly increasing RPM. The most easily overlooked issue is leaks in the fuel vapor system - even a cracked charcoal canister hose can cause unstable idle. A simple solution is to turn off the engine, wait a few minutes, and restart to let the ECU perform a fresh self-check.
