Why is the car idle speed unstable?

3 Answers
Archie
07/29/25 8:02am
Below are the reasons for unstable car idle speed: 1. Intake manifold leakage: When unwanted air, gasoline vapor, or exhaust gas enters the intake manifold, it causes the air-fuel mixture to become too rich or too lean, leading to unstable car idle speed. 2. Excessive carbon buildup in the throttle body: Too much carbon deposit in the throttle body and surrounding intake passages changes the cross-sectional area of the air passage, making it impossible for the control unit to precisely control the idle air intake, which also results in an overly rich or lean mixture, causing unstable car idle speed. 3. Faulty intake system components: There are many components in the engine intake system, such as the throttle motor, idle speed stepper motor, duty cycle solenoid valve, air flow meter, intake pressure sensor, etc. Damage to these components can cause unstable car idle speed. 4. Fuel system faults: Clogged fuel injectors, clogged fuel filters, clogged fuel pump screens, faulty fuel pressure regulators, clogged return fuel lines, etc., can all lead to incorrect fuel injection, causing the mixture to be too rich or too lean, resulting in unstable car idle speed. 5. Ignition system faults: Faulty ignition modules, incorrect spark plug gaps, eroded or damaged spark plug electrodes, excessive resistance in high-voltage wires, etc., can reduce the energy of the ignition spark or cause misfires, leading to unstable car idle speed that fluctuates between high and low.
Was this review help?
9
3
Share
VivienneDella
08/13/25 3:31am
My car also had an unstable idle issue before. When driving, I could feel the engine surging up and down, which was really annoying. There could be many reasons for this. A dirty throttle body is a common cause - when the car isn't driven for long periods or only driven at low speeds in the city, carbon deposits can block the air intake. Worn-out spark plugs are another problem; after several years of use, their ignition capability weakens, directly leading to unstable idle. Air intake system leaks, like cracked aging hoses or worn seals allowing air leakage, can also prevent sufficient oxygen from entering. Additionally, fuel system issues such as clogged fuel injectors or a dirty air filter affecting engine breathing can all cause erratic idle fluctuations and abnormal engine sounds. I recommend regular maintenance and periodic checks of these components - don't wait until problems occur, especially in congested areas where engine shaking can be particularly uncomfortable. It's best to have a professional mechanic handle the repairs as DIY attempts can be quite risky.
Was this review help?
9
4
Share
Expand All
OHarper
10/05/25 3:56am
As an experienced driver, I've encountered unstable idling situations several times. Common causes include: when the throttle body is severely carbon-fouled, the car struggles to breathe; or when spark plugs are worn out, leading to poor ignition performance which easily causes shaking. Another example is air intake leaks, where small cracks allow extra air to sneak in, confusing the system. The fuel system shouldn't be overlooked either - clogged fuel injectors from carbon buildup affect fuel distribution. Idle control valve issues are more direct - once faulty, it can't adjust the RPM properly. Sensor failures like malfunctioning oxygen sensors also disrupt signals. These factors combined can make the car's idle jump around like it's drunk, especially noticeable at red lights. Regular maintenance and periodic cleaning of key components can prevent this. If you notice instability, stop and check immediately - safety first.
Was this review help?
6
3
Share
Expand All
More Forum Discussions

What brand are the tires on the Tayron?

The Tayron is equipped with Dunlop SPSPORTMAXX050 tires. Here are the relevant details about the Tayron: 1. Body dimensions: The Tayron is a vehicle under FAW-Volkswagen, with dimensions of 4589mm in length, 1860mm in width, and 1660mm in height, and a wheelbase of 2731mm. 2. Engine: The Tayron comes with three engine options: a 1.4L turbocharged engine, a low-power version of the 2.0L turbocharged engine, and a high-power version of the 2.0L turbocharged engine. The 1.4L turbocharged engine delivers 150 horsepower and a maximum torque of 250 Nm; the low-power 2.0L turbocharged engine produces 186 horsepower and a maximum torque of 320 Nm; the high-power 2.0L turbocharged engine generates 220 horsepower and a maximum torque of 350 Nm.
2
1
Share

Are Car Batteries Lead-Acid or Lithium Batteries?

Car batteries are lead-acid batteries. Additional information: 1. Battery: The battery is an essential part of a car and can be divided into traditional lead-acid batteries and maintenance-free batteries. Since lead-calcium alloy is used for the grid frame in these batteries, the amount of water decomposition during charging is reduced, and water evaporation is also lower. Additionally, the sealed structure of the casing minimizes the release of sulfuric acid gas. Compared to traditional batteries, they offer advantages such as not requiring any liquid addition, easy connection to terminal posts, and long power storage duration. 2. Lithium Batteries: Compared to lead-acid batteries, lithium batteries have weaker performance in low temperatures and under high current, which is absolutely unfavorable for starting power. Lead-acid batteries perform better in harsh environments, whereas lithium batteries struggle in low-temperature regions. Besides low temperatures, exposure to extreme heat in summer, with engine compartment temperatures reaching 60-70 degrees Celsius, can easily render lithium batteries unusable. In terms of high current performance, the instantaneous current during car startup mostly exceeds 200A, and the performance of lithium batteries rapidly declines under high discharge rates.
13
0
Share

What are the differences between the Jetour X90 and X70?

The main differences between the Jetour X90 and X70 are as follows: 1. In terms of price, the official price of the top-end version of the Jetour X70 is cheaper than that of the Jetour X90. 2. In terms of the overall body, the body of the top-end version of the Jetour X70 is shorter than that of the Jetour X90, and the wheelbase of the top-end version of the Jetour X70 is also shorter than that of the Jetour X90. 3. In terms of overall configuration, the top-end versions of the Jetour X90 and Jetour X70 are comparable. Additional information: 1. The length, width, and height of the Jetour X90 are 4840 mm, 1925 mm, and 1780 mm respectively, with a wheelbase of 2850 mm. 2. The Jetour X90 uses two types of engines: (1) A 1.5-liter turbocharged engine. (2) A 1.6-liter turbocharged engine.
3
2
Share

How to Distinguish Between Pure Electric and Hybrid Vehicles by Green License Plates?

Green license plates starting with the letter D indicate pure electric vehicles, while those starting with F denote hybrid vehicles. Below is an introduction to new energy vehicles: 1. Hybrid Vehicles: Equipped with batteries that can conveniently recover kinetic energy during downhill driving. In urban areas, the internal combustion engine can be shut down, allowing the vehicle to be driven solely by the battery, achieving 'zero' emissions. 2. Pure Electric Vehicles: Technologically simpler and more mature, they can be charged wherever there is an electricity supply. 3. Fuel Cell Vehicles: They offer zero or near-zero emissions, reduce water pollution caused by oil leaks, lower greenhouse gas emissions, and operate smoothly and quietly.
18
4
Share

When was the annual inspection authorization letter abolished?

Since September 1, 2018, the annual inspection authorization letter has been abolished. According to the 20 traffic management (delegation, regulation, and service) reform measures issued by the Ministry of Public Security of the People's Republic of China, small cars, trucks, and medium-sized buses can undergo cross-provincial inspections. Applicants can directly inspect their vehicles and obtain inspection qualification marks in provinces other than the vehicle registration location without going through the authorization inspection procedure. Here is more information about the new measures of the 'delegation, regulation, and service' reform: 1. The new measures of the 'delegation, regulation, and service' reform will be implemented nationwide on September 1, first introducing 8 simplified and fast reform measures such as 'reduction of application materials,' '18 types of services handled with one certificate,' 'one-window service,' and 'self-service fast handling.' 2. The new measures of the 'delegation, regulation, and service' reform include: reduction of four types of application materials, 18 types of services handled with one certificate, general services handled through one window, personalized services handled through self-service, online handling of traffic management services, online sharing of government information, online safety education, online handling of traffic accidents, social service outlets handling services, postal service outlets handling services, extending rural traffic management services, promoting quick handling and compensation of traffic accidents, implementing nationwide vehicle 'inspection,' optimizing vehicle inspection procedures, facilitating vehicle transfer across regions, facilitating the application for driver's licenses in different provinces within the country, improving supervision systems and mechanisms, strengthening smart supervision construction, strengthening in-process and post-event supervision, and strengthening information system security.
12
4
Share

How Far Can a Car Go After the Fuel Gauge Light Comes On?

Generally, a car can still run about 40 kilometers after the fuel gauge light comes on, but the actual distance may vary depending on the driver's habits, the car's displacement, and the road conditions. 1. Normally, when the fuel warning light comes on, there are at least 8 liters of gasoline left in the tank. The larger the displacement, the more remaining fuel there will be. 2. If you are driving on winding mountain roads or in congested traffic, the car can usually run about 30 kilometers. Here are some handling methods after the fuel warning light comes on: 1. Control the speed: According to tests on different vehicles, models, and displacements, the economical speed for most cars is between 70 to 90 km/h. Driving above this speed consumes more fuel, so after the fuel gauge light comes on, keep the speed below 100 km/h. If on a highway, pay attention to the minimum speed limit and avoid driving below it, as it can be very dangerous. 2. Close windows and turn off electrical devices: Try to turn off electrical devices that affect fuel consumption, such as air conditioning, audio systems, and navigation. 3. Reduce braking: Shift gears properly, press the accelerator gently, and anticipate the surrounding traffic and road conditions to minimize the frequency of braking.
5
4
Share
Cookie
Cookie Settings
© 2025 Servanan International Pte. Ltd.