Why is my car idling rough? Answers from Des Moines' best auto repair
The engine shudders at the red light and you wonder if it will die before it turns green.
You're right that it's a problem. Misfires, dirty fuel or air parts and weak ignition parts are the usual causes.
Not safe to drive if you notice
- Engine stalls in traffic
- Flashing check engine light
- Fuel smell
Visit the shop
- 5875 Fleur Drive, Des Moines, IA 50321
- Monday – Friday: 7:30 AM – 5:00 PM
- 515-745-0934
Is it safe to drive when experiencing rough idle or stalling?
Usually yes. A rough idle with a car that otherwise drives normally can usually wait for a visit soon. If the engine stalls, especially in traffic, stop driving it and have it checked.
Usually safe to drive
- The idle feels a little shaky at stoplights.
- The RPM needle bounces slightly at idle.
- The car accelerates and drives normally once moving.
- The check engine light is off or steady.
Not safe to drive
- The engine stalls at stops or in traffic.
- The check engine light is flashing.
- The engine stumbles or loses power when you press the gas.
- You smell fuel or a strong rotten egg odor.
- The temperature gauge climbs or another warning light comes on.
Not safe to drive? Stop and call us now.
Pull over somewhere safe and call Joey's Auto Shop at 515-745-0934. We'll help you figure out your next step.
Why an engine idles rough or stalls
A rough idle means the fuel, air, or spark the engine needs is off.
Worn spark plugs
Worn plugs cause misfires that make the engine shake at idle.
You need Spark PlugsFailing ignition coil
A bad coil cannot fire its plug, which causes a misfire.
You need Ignition Coil ReplacementDirty fuel injectors
Dirty or clogged injectors cannot deliver fuel evenly.
You need Fuel Injection RepairIntake carbon buildup
Carbon on the intake valves is common on many direct-injection engines and upsets the idle.
You need Intake Carbon CleaningAirflow sensor or vacuum leak
A dirty mass airflow sensor or a vacuum leak throws off the air reading.
You need Mass Airflow SensorSticking EGR valve
An EGR valve that sticks open can make the engine stumble at idle. A weak fuel pump or clogged fuel filter can do the same.
You need EGR Valve Service
What you can check first
A few things you can notice before your visit:
Note whether it shakes at idle, when accelerating, or both.
Watch whether the RPM needle bounces at a stop.
Note whether the check engine light is off, steady, or flashing.
Remember whether it stalls when cold, warm, or coming to a stop.
Notice any drop in gas mileage.
Ready for a smooth idle again?
Call Joey's Auto Shop, a Des Moines People's Choice Winner 2022 through 2026, or make an appointment and tell us what's going on.
We find the cause, not only the symptom
The fix can be new plugs, a coil, an injector cleaning, or a sensor. The shop tests first, so you only pay for the part that is causing it.
- Step 1
We test
The shop scans for codes, looks at live engine data, and tests ignition, fuel delivery, and air intake until it finds the fault.
- Step 2
We show you
You get a digital inspection with photos and notes in plain language, so you see what we see.
- Step 3
You decide
Nothing starts until you approve it, and we confirm the fix before you pick up your car.
Why not ignore a rough idle?
Misfires waste fuel and can overheat and damage the catalytic converter, which is a costly part to replace. Stalling in traffic is a safety risk. These problems tend to get worse, not better. Catching a rough idle early usually means a smaller fix, such as new spark plugs or a coil, before other parts get damaged.
Can a fuel pump or fuel filter cause stalling?
Yes. A weak fuel pump or a clogged fuel filter can starve the engine of fuel, especially at idle or under load. The engine may stumble when you press the gas, or die when you come to a stop. Testing fuel delivery shows whether the pump and filter are keeping up with what the engine needs.
What is carbon buildup on intake valves?
On many direct-injection engines, fuel is sprayed straight into the cylinder instead of over the intake valves. Without fuel washing over them, carbon slowly builds up on the valves. Over time it restricts airflow and can cause a rough idle, hesitation, and misfires. An intake carbon cleaning removes the buildup.
What is a vacuum leak?
The engine measures the air coming in so it can add the right amount of fuel. A vacuum leak is a crack or loose fitting that lets extra air in after that measurement. The engine then runs with too much air and too little fuel, which can cause a rough idle, a high or bouncing idle, or stalling.
Other symptoms we can help with
See All Symptoms
Check Engine Light Is On
A steady or flashing check engine light means your car's computer found a problem. Some causes are small. Some get expensive if you wait.
Learn More
Car Shakes or Vibrates
A shake in the steering wheel, seat, or brake pedal can come from your tires, brakes, suspension, or engine.
Learn More
Shaky at idle?Let's smooth it out.
Make an appointment and tell us what's going on. We explain your options before any work begins.