What Are the Causes of High Engine Idle Speed?
2 Answers
The causes of high engine idle speed are: 1. Throttle valve sticking or not closing properly; 2. Additional air valve malfunction; 3. Idle speed control valve malfunction; 4. Water temperature sensor malfunction; 5. Air conditioning switch or power steering pressure switch malfunction; 6. Crankcase forced ventilation valve malfunction; 7. Intake system air leakage; 8. Generator charging voltage too low. The reasons for low engine idle speed are: 1. Throttle valve partially dirty or excessive carbon buildup, cleaning required; 2. Stepper motor malfunction; 3. Fuel line or fuel supply pressure issues; 4. Electronic fuel pump malfunction; 5. Internal engine malfunction; 6. Spark plugs, ignition wires, or distributor damage.
Last time I started my car, the tachometer shot straight up to over 2000 rpm, the idle speed was terrifyingly high. It might be that the throttle body is clogged with dirt restricting airflow, like dust or oil buildup suffocating the engine; or a cracked vacuum hose leaking air into the system, tricking the computer into thinking it needs to enrich the fuel mixture; or perhaps the idle control valve is stuck or a sensor malfunctioning, like the temperature sensor misreading that the engine is still cold in winter and aggressively revving. This leads to skyrocketing fuel consumption - I paid hundreds more on gas last month, plus it worsens emissions polluting the environment. You could first try disconnecting the battery negative terminal to reset the ECU, or wiping the throttle body with a cloth. If that doesn't fix it, visit a professional shop before getting stranded roadside.
