What Causes Erratic Idle?

What can cause a fluctuating idle?

Erratic engine idle can be caused by various factors, but the most common and likely cause is a dirty or malfunctioning Mass Air Flow (MAF) sensor.

Although it is positioned after the air filter, over time, contaminants can build up on the sensor..

Why does my car rev up and down while idling?

The idle is controlled by the idle air control valve and if it cannot keep the engine idling it will keep trying to rev the engine up to compensate. A vacuum leak, sensor that has failed, or an EGR system malfunction could potentially be the cause of the erratic engine you’re experiencing.

What is a surging idle?

Copyright AA1Car. If a vehicle idles erratically and surges (idle speed is not steady and increases and decreases), the problem may be a buildup of carbon or fuel varnish deposits in the idle speed control valve (also called the idle air control valve or IAC valve).

What does surging mean?

1 : to rise and fall actively : toss a ship surging in heavy seas. 2 : to rise and move in waves or billows : swell the sea was surging. 3 : to slip around a windlass, capstan, or bitts —used especially of a rope. 4 : to rise suddenly to an excessive or abnormal value the stock market surged to a record high.

What does engine surging feel like?

You may notice the tachometer fluctuating, for example, from 1500 to 2000 rpm. At the same time, you may feel a soft and rhythmic jerking motion. The problem may come from a faulty sensor or system that is making the computer deliver too much or too little fuel, and then try to correct the fault by over-compensating.

Why does my car vibrate when idle?

Motor Mounts. Motor mounts keep your engine attached to the car. Weak or broken mounts can’t hold the engine tight in the engine compartment and creates a vibration at idle. If the shaking subsides when the car is in Neutral, this could indicate the motor mounts are responsible for the vibrations.

Why my rpm goes up and down?

Hi There, It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate. … When this happens, the job of the idle air control valve is to bring this deceleration down to a slow and smooth idle rather than suddenly cutting off the fuel supply causing the motor to die.

Is it normal for RPM to fluctuate at idle?

It actually is completely normal for the engine idle speed fluctuate a small amount. … That is a lot to ask the engine to do at a very low rpm.

What are the symptoms of a bad idle control valve?

Common signs include irregular or unusually high idle speed, the Check Engine Light coming on, and stalling while idling.

What does engine surging mean?

Engine surging is when an engine starts easily and accelerates smoothly, however after a few minutes at a steady speed, it either surges in speed or misfires. Misfiring happens when one of the cylinders of an engine’s combustion cycle fails.

What should rpm be at idle?

For a passenger car engine, idle speed is customarily between 600 and 1000 rpm. For medium and heavy duty trucks, it is approximately 600 rpm. For many single-cylinder motorcycle engines, idle speed is set between 1200 and 1500 rpm. Two-cylinder motorcycle engines are often set around 1000 rpm.

Why does my car shake on idle?

Worn out spark plugs are one of the most common causes of engine shaking. If your spark plugs are dirty or worn out they will be unable to fire properly and create the spark your engine needs to ignite the fuel. … Replacing your spark plugs is typically inexpensive.