Skip the auto shop - Our mechanics make house calls

Q: Idle fluctuates

asked by on

It shutters and idles rough between 0 -500 rpm in idle. The Instrument panel flikkers and the radio turns on and off. What should I do?

My car has 169456 miles.
My car has an automatic transmission.

Hi There, It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate. The idle air control valve is a small valve on the engine’s intake system that reads the air intake as it comes into the motor. This is controlled by the car’s ECM which uses this information to make adjustments to the air/fuel ratio depending on various inputs such as outside air temperature, intake air temperature, load and various other things. As you accelerate, your car’s engine is receiving a much higher dose of fuel than when at idle and conversely, when you let off the gas pedal, there is a sudden change in this fuel supply as a result of your foot letting off the pedal. 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. When the idle air control valve is not working properly, this cause a disruption in this process resulting in the engine not being able to idle properly. As this fluctuation in idle happens, this may also cause the charging of the alternator to fluctuate slightly as well resulting in the lights flickering or dimming slightly as the engine RPM drops. I would recommend having a professional come to your location to diagnose and inspect your vehicle.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Idle fluctuates

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Bank 1 and Bank 2 running lean

If lean faults occur after the manifold was removed and reinstalled, this indicates a vacuum leak which also means that unmetered air is coming into the intake. Either a vacuum line or induction pipe is loose, or the manifold is...

Q: 2003 mitubishi eclipse spyder gts v6 3.0 what is the best mounts for this car

Hi there. For Mitsubishi or any other vehicle, it's always recommended to replace older engine and transmission mounts with OEM parts. In fact, I would not recommend any aftermarket components for mounts or bushings.

Q: Car not shifting into lower gears

Hi. If the transmission is shifting fine when it is in gear, but the shifter will not achieve all positions then most of the time it is caused by a binding shift cable. A certified mechanic would typically start by...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...