Why Can't the Idle Speed of 1800 RPM Be Reduced?
4 Answers
The reason why the idle speed of 1800 RPM cannot be reduced is excessive carbon deposits in the throttle valve, intake manifold, intake valves, and combustion chamber. Excessive Carbon Deposits: Due to excessive carbon deposits and dirt in the intake manifold, the cross-sectional area of the air passage changes, making it impossible for the control unit to precisely control the idle air intake. This results in an overly rich or lean air-fuel mixture, causing abnormal combustion or engine shaking after startup, and even failure to start. High Idle Speed: When the idle speed exceeds the set RPM, the ECU commands the idle control valve to reduce the intake bypass, decreasing the air intake and lowering the engine speed. Issues such as sticking of the idle control valve due to oil sludge and carbon deposits or incomplete closing of the throttle valve can prevent the ECU from correctly adjusting the engine's idle speed, leading to unstable idling.
My car's idle speed is stuck at 1800 RPM and won't come down, which is quite annoying. When driving normally, I feel the RPM is abnormally high. This could be due to excessive dirt buildup in the throttle body preventing air from entering, causing the RPM to stay high, or the idle control motor might be stuck and not working. Another possibility is a faulty mass air flow sensor sending incorrect signals, leading the engine computer to mistakenly maintain high RPM. Additionally, aging or cracked vacuum lines leaking extra air is a common cause. Having such a high idle speed not only wastes fuel and money but also accelerates engine wear over time, shortening its lifespan and increasing noise. I tried fixing it myself before without success, but in the end, I took it to a professional repair shop. The mechanic used a diagnostic tool to check the trouble codes and completely resolved the issue, saving me a lot of hassle. Safety first.
I have considerable experience dealing with high idle issues at 1800 RPM. The most common cause in older vehicles is vacuum system leaks from cracked hoses allowing unmetered air intake. A faulty throttle position sensor can trick the ECU into maintaining higher RPMs. Sticking or dirty idle air control valves, or ECU programming glitches (common in modified cars) may also cause this. Persistent high idle wastes fuel, causes overheating and accelerates engine wear. The fix isn't complicated - first check vacuum lines with the hand-over-intake method, clean throttle components, replace faulty parts promptly to avoid collateral damage and unnecessary repair costs.
My car's idle speed stays at 1800 RPM and won't drop, likely due to ECU tuning issues which are common with improper modifications. Dirty mass airflow sensors sending erratic signals, vacuum leaks, or stuck idle control valves can all cause persistently high RPMs. This wastes fuel, affects acceleration smoothness, and reduces performance. I often try cleaning the sensors myself to save money, but professional inspection is more reliable.
