Skip the auto shop - Our mechanics make house calls

Q: Engine idle fluctuates and dies.

asked by on

When I come to stop at a red light my rpm doesn't go lower than 1 and when this happens ( which is always) it gives me a big kick then stalls. Also when I start it up in the morning the rpm goes straight to 3 and stays there until I put it in drive. Then when I do this it doesn't by go lower than 1rpm . Why are these things happening???

My car has 200503 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 and eventually stall. In the mornings it is normal for the engine idle to be a bit higher than normal when you start the car as this is the cold start enrichment process which allows the engine to warm up sufficiently, however this should cause the RPM’s to hover around 1,200-1,500 or so, not 3,000.

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. 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

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: It's been raining heavly, and now I've got water coming through the flooring in my car, I haven't passed my driving test yet so it

Hello, thank you for writing in. The vehicle is likely going to need an inspection before knowing what the real cause of the water leak is. Rust can certainly accumulate on the bottom of the vehicle and allow water to...

Q: Fuse box wires burned

Hi. The issue you have experienced demands a mechanic's attention. The fuse box is the power unit to most of your main power sources in your vehicle. The burned wires are caused by overheating to a point where the wires...

Q: Cruise control has not been working for a while.

Hi there. First check to see if the cruise control fuse is blown. Then check the brake light switch, the brake pressure switch, the speed sensor on the transmission, or the cruise control buttons. Most of the time the brake...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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.