What Causes High Idle Speed in Nissan Bluebird?
3 Answers
There are three main reasons for high idle speed in Nissan Bluebird. Idle switch not closing: The rotation speed signal determines the fuel injection volume and injection timing. When the engine is operating under idle conditions with reduced air intake, this leads to an over-rich air-fuel mixture and consequently increased engine speed. Malfunctioning idle control valve: When the idle speed exceeds the preset value, the ECU commands the idle control valve to reduce the bypass air intake, thereby decreasing engine speed. Issues like sticking due to oil contamination/carbon buildup or incomplete throttle valve closure can prevent the ECU from properly regulating idle speed, resulting in unstable idling. Intake manifold air leakage: The opening degree of the idle control valve and air intake strictly follow a specific functional relationship - increased valve opening corresponds to greater air intake. Air leakage disrupts this relationship, making the air flow sensor unable to measure actual intake volume accurately. This causes imprecise ECU air intake control and unstable engine idle.
My Bluebird has a high idle speed, and I've seen this a lot over my years of repairing cars. The main cause is carbon buildup in the throttle body getting stuck, which increases the intake air and raises the RPM. Problems with the idle control valve are also common—if it's dirty or faulty, the control goes haywire, leading to unstable idle. Air system leaks, like cracks in vacuum hoses, can also be an issue, as the engine draws in extra air. Faulty sensors, such as the idle position sensor, send inaccurate data, causing the ECU to issue wrong commands. A high idle during cold starts is normal, but if it stays high, it's dangerous and affects braking and control. I suggest first checking if the engine light is on, then getting the throttle body cleaned and the control valve inspected. This is a common issue with older cars—spending a little to fix it saves both peace of mind and fuel.
I drove a Nissan Bluebird for over ten years, and one time the idle speed suddenly surged. Even without pressing the accelerator pedal, the tachometer shot up rapidly, which really startled me. After it was fixed, I learned that the throttle body was clogged with carbon buildup. When too much carbon accumulates, it can get stuck in the open position, increasing the air intake. If the idle control valve is aged or dirty, it won't function properly, and replacing it with a new part will fix the issue. In some cases, a leak in the intake manifold can cause air to escape, leading to a runaway idle speed. If you're not familiar with car repairs, it's best not to tinker with it yourself. Take it to a 4S shop and let the technicians diagnose it—they can quickly identify the issue with a computer scan. High idle speed wastes fuel and damages the engine, so it's safer to address it promptly.
