The unstable idle speed of car is mainly manifested in fact that tachometer needle goes up and down at idle, and guidance is unstable, fluctuates up and down, and idle speed is unstable, accompanied by jittering idle speed. Erratic idle is actually one of most common engine faults, with faults ranging from major to minor. Under normal conditions, engine idle speed is fixed, and specific altitude depends on specific car model. Generally speaking, if idle speed is high, fuel consumption will be relatively high, but if idle speed is too low, engine may vibrate or even stall. The following editor provides an analysis of 9 common causes of engine idle speed control system failure for reference.
1. Insufficient power generation of generator at idle leads to electromagnetic interference
Insufficient power generation at idle will cause non-linear distortion of alternator signal, and generated electromagnetic interference will affect fuel injector, causing engine to shake slightly at idle, and it will return to normal after starting.
2. When engine speed is below 1500 rpm, power is insufficient
Generator signal non-linear distortion sometimes affects ignition sensor, causing ignition sensor to erroneously send an ignition signal, causing engine ignition timing to be too late, resulting in apparent insufficient engine power at idle. and a light load causing vibration at idle and slightly poor acceleration under load.
3. I feel heaviness when I press accelerator pedal for first time in a day
① If idle stepper motor and idle control valve are too dirty and stuck, you will feel heaviness when you press accelerator pedal for first time every day. In severe cases, you need to lightly press accelerator pedal to complete start.
② Fully release accelerator pedal while driving, stop fuel injection into engine, and start stepper motor to resume fuel injection when engine speed drops to 1500 rpm, but direct-flow idle throttle control system sticks due to excessive soot. The idle control valve of bypass idle control system is too dirty and stuck, causing stepper motor not to start in time, causing engine to overload and stop, and in severe cases, it will cause car to stall when driving on low speed.
Note. An easy way to determine if idle control system load variation control is working properly is if A/C is used, automatic transmission is on, or power steering is being used while engine is idling, engine idle should rise slightly. engine speed drops by more than 50 rpm, idle speed control system should be checked.
4. Erratic idle
The reason for unstable idle speed is that idle stepper motor is too dirty or fuel injector is blocked. The main reason for early clogging of injectors is too low fuel quality, as well as high olefin content in low-grade fuel.
5. Fault tolerance for wear parts of an idle stepper motor
When number of steps of stepper motor controlled by control box does not reach control effect, control box will control according to feedback signal from crankshaft speed sensor.
6. Solving problem of unstable idling of engine with electronic throttle
(1) Clean electronic choke regularly
The idle speed of vehicles equipped with an electronic throttle is unstable, in most cases this is caused by contamination of electronic throttle. Once electronic throttle valve is seriously contaminated with dust, it will lead to unstable engine idling, poor vehicle acceleration, heavy accelerator pedaling, increased fuel consumption, excessive exhaust emissions, and in severe cases, burnout at idle, but stable operation at medium and high speeds. . The electronic throttle body is usually cleaned every 40,000 km of car.
(2) Electronic choke general initialization method
① Disconnect negative battery before cleaning;
② Connect negative pole of battery after cleaning;
③ For Honda models: turn on ignition for 30 seconds, then turn it off for 15 seconds to complete electronic throttle initialization;
④ For Toyota vehicles: turn off ignition, disconnect EFI and ETCS fuses in fuse box in engine compartment, and install them after 1 minute to complete electronic throttle initialization;
⑤ For Chrysler series, turn ignition key to ON, turn on power but do not start engine, ignition key should be held in ON position for at least 10 seconds, and PGM will use this time. complete self-adaptation of electronic throttle;< /p>
⑥ For Mitsubishi vehicles, turn on ignition for 1 second, then turn it off for 15 seconds to complete electronic throttle initialization;
⑦ For Citroen series vehicles, turn ignition key to M for 30 seconds (be careful not to depress accelerator pedal), then turn off ignition key for 15 seconds to complete electronic throttle initialization. .
(3) Intake system leak detection method
The leakage from intake system is mainly concentrated at junction of vacuum hose, bellows and throttle valve. Use a vacuum gauge to check degree of vacuum in intake system of engine at idle. If degree of vacuum in intake tract at idle is below 17.8 kPa, you need to focus on checking for leaks in intake system. .
Note. When front engine mount cushion is broken, it will cause engine to vibrate at 1500 rpm idle, and if it is serious, it will affect knock sensor, resulting in insufficient power at light load. .
7. The air flow sensor terminals on both sides of V-motor are connected incorrectly
During this time, engine may shake at idle, exhaust gases will choke, and exhaust pipe on one side will turn red. If it is not reinstalled in time, it can lead to ablation of three-way catalytic converter.
8. Poor sealing of engine intake system with an air flow sensor
The engine idle speed on air flow sensor is stable on a cold car, and idle speed shakes after car warms up (thermostat fan starts to rotate), which indicates intake of unmetered air in intake hose, resulting in a too lean mixture. Read oxygen sensor data stream. At this time, output voltage is only 0.03V. The most likely cause is a leak in intake system. The focus should be on checking if there is a crack in joint on intake manifold. side of vacuum hose and whether there is a clip on bellows on side of throttle valve.
9. The engine shakes a lot at idle, after high idle it runs smoothly
The focus should be to check for a malfunction of 24X crankshaft position sensor. The 24X crankshaft position sensor is responsible for smooth operation of engine at a speed below 1200 rpm.
What's wrong with unstable idle speed? Solution
Causes of instability of idle speed of car: hole of idle air volume is clogged, idle device does not work well, spark of spark plug of some cylinders is too weak, some valves are leaking, intake manifold is leaking, ignition time is too long. Too early or too late ignition, incorrect idle speed adjustment, etc.
The most direct way to adjust idle speed is to adjust idle speed and have engine run at a minimum stable speed by adjusting throttle opening adjustment screw. Before adjusting idle speed, a number of vehicle checks must be carried out, such as normal engine temperature, correct valve clearance, normal ignition system, good sealing of all pipes, full opening of choke and tight closing. throttle body.Operation, it is best to go to a professional repair shop or 4S shop to adjust.