What Causes High Idle Speed in Cars?
3 Answers
The reasons for high idle speed in cars are: 1. The idle switch does not close; 2. Malfunction of the idle control valve; 3. Air leakage in the intake pipe; 4. Incorrect valve timing; 5. Fuel injector dripping or clogging; 6. Blockage in the exhaust system; 7. The EGR valve opens during idle conditions. The solutions for high idle speed in cars are: 1. Check the throttle opening; 2. Check the engine load signal; 3. Check the vacuum level in the intake manifold; 4. Reset the engine control unit; 5. Check whether the throttle is fully closed during idle and if the throttle cable is stuck; 6. Readjust the idle program; 7. Check for air leaks at the intake system pipe joints and vacuum hoses; 8. Perform fault self-diagnosis; 9. Check the coolant temperature sensor; 10. Check the crankcase forced ventilation valve.
I know all too well about the issue of high idle speed in cars! There are four common causes: First, the throttle body is dirty, with too much carbon buildup preventing the valve from closing properly, leading to inaccurate air intake control. Second, there's a leak in the intake pipe, like aging or cracked rubber hoses, allowing air to bypass the sensor. Third, the coolant temperature sensor is faulty, sending false signals to the ECU, making the engine think it's in the cold start phase. Lastly, it could be a stuck idle control valve, as if glued with 502 adhesive, unable to move. What annoys me most is that if left unrepaired, fuel consumption can increase by 20%, the exhaust pipe emits black smoke, and over time, the catalytic converter suffers.
Noticed your car's idle RPM won't come down? My car did the same thing last week! Simply put, it's a failure in the computer-controlled air intake. Either the throttle cable is too tight and stuck in position, or the AC compressor kicked in and increased the engine load. The key is to check the dashboard's coolant temperature gauge—if the RPM stays high at normal temperature, further troubleshooting is needed. I once cleaned the throttle body myself; carbon deposits and sludge were stuck around the valve plate, and a few sprays of specialized cleaner fixed it. Another sneaky issue is a loose air flow meter connector—just a slight touch can cause poor contact. That thing is super sensitive; even car wash water spray can make it act up.
