Why is the car shaking while idling

Car engine idling speed is lower than or beyond the prescribed range, causing engine stalling intermittently, unstable idling speed and other symptoms.

1. How to deal with unstable idling speed

The symptoms of unstable idling speed: the engine is shaking and the idle speed is unstable while idling. The causes are as follows: idle air valve is clogged, it can not work. Well, some spark plugs is too weak, valve sealing is poor, intake manifold leakage, ignition timing is too early or too late, improper adjustment of idle, etc.

If idle speed is not stable, first of all, adjust the idle speed. If the fault still cannot be eliminated after the idle speed adjustment, check the idle speed and idle air jet. If the idle air jet is clogged, clean it with gasoline or acetone and compressed air blow through. If the fault is still not removed, check the intake manifold or carburetor, whether there is leakage on the gasket. If there is, tighten screws or add, reduce gasket to eliminate the fault. If the idle speed is unstable and accompanied by the phenomenon of engine power decline, it should further check the spark plug, valve sealing performance and ignition timing. If necessary, should be repaired or adjusted.

2. How to distinguish bad idling speed

A normally functioning engine should be able to operate uniformly within a speed range of 500-800r/min. If the minimum stable speed of the engine exceeds this speed range, or within this speed range, the engine has stalled, unstable speed, indicating your car have a bad idling speed. According to its fault characteristics, the faults can be divided into three types: engine flameout while idling, unstable engine idle speed and high idle speed. 

(1) If the engine has been started, no matter it is running well at low speed or high speed, once release accelerator pedal, the engine stalls immediately, or running unstably and then stall. 

(2) If the engine idle speed is not smooth, the exhaust pipe send off  "chug" sound, it generally is caused by instability of the engine's idle speed. 

(3) If the idle speed of the engine is higher than the specified range, and cannot slow it down, it is considered as too high idle speed. 

3. How to adjust idle speed

The adjustment of idle speed must be carried out under normal conditions, such as normal engine temperature, proper valve clearance, normal ignition system, good pipe sealing, strangler to the full open position and tight closure of throttle valve. When adjusting, first unscrew the throttle opening adjustment screw, so that the engine to reach the minimum stable speed. Then use a screwdriver to screw tightly the idle speed adjustment screw, when the engine is about to shut off, then slowly unscrew the idle speed adjustment screw, so that the engine stable operation and reach high speed. The process is repeated up to several times, until the throttle opening to a minimum, the engine operates at a minimum of steady speed. At last, increase the idle speed and suddenly close the throttle, the engine is not shut off as appropriate.

4. Engine flameout while idling

The idle speed should be adjusted according to the actual situation. After adjustment, if the fault disappears, means improper adjustment of idle screw. If we have checked the adjustment of idle screw, excluding the possibility, we can adjust the throttle opening to keep the engine running. Then check the air intake manifold gasket and carburetors (old mode) whether is leakage, if not, check idling air jet, ensure idle oil duct is smooth. If the fault doesn’t exist at this moment, indicates the idling air jet and oil duct is clogged. For carburetors equipped with idle globe valve, check whether the solenoid coil circuit of idle globe valve is normal. If the idle globe valve is blocked due to abnormal solenoid coil circuit, the idle globe valve should be repaired.

 5. What if the idle speed is too high

When the idle speed is too high, the engine should be started first, and then manually control the throttle arm, so that the throttle valve is closed. If the idle speed is normal, the throttle tension spring is weak and should be replaced. If closing the throttle valve by hand is invalid, check whether the throttle shaft is loose or tight. If the throttle shaft is loose, repair shall be performed. If the throttle is normal, check whether there is slight air leakage under the throttle. If so, eliminate the air leakage. If not, further adjust the idle speed until the idle speed is appropriate.

James Smith        October 26, 2020

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