Skip the auto shop - Our mechanics make house calls

Q: Idle fluctuates and then stalls.

asked by on

My car won't always start the first time you turn the key in the ignition. The dashboard says the engine has reduced power, the rpm's jump erratically while driving. Occasionally the dies while driving engine dies and the car stops. Most recently I had to jump start because it would not start at all when I got in it.

My car has 108000 miles.
My car has an automatic transmission.

It sounds like you may have a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic 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!

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: Stopped at red light, when turned green car wouldn't accelerate only reverse

Hi There, What you are describing is often a sign of low transmission fluid or a faulty transmission control solenoid. As you know, automatic transmissions use pressurized hydraulic fluid to change gears. Every time a gear change is required, the...

Q: 4l60e transmission runs fine until engine warms up then loss of all gears and metal on metal noise from bell housing. What do I do

Hi Mike. Anytime you hear metal to metal coming from inside the bell housing of an automatic transmission, that's typically an indication of damage to the torque converter or flywheel. With 300,000+ miles on your Silverado, it's probably time to...

Q: Headlight stopped working

Hi there. Sounds to me that you have a power to ground short somewhere in your headlight wiring. Have a certified mechanic further diagnose your headlight issue in person.

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.