Car idles rough refers to when an automobile’s engine runs too slowly or it runs erratically while disconnected from a load or out of gear. This video details the probable causes and corrections needed to fix a car that idles rough. These service procedures also pertain to vehicles that idle rough and stall.
Car idles rough
1. 0:27 Carbon build-up on throttle plate. If there is excessive carbon build-up or dirt and grime on the throttle plate, the plate will not return to its correct position fast enough and it will cause an air to fuel ratio imbalance. When there’s an imbalance to the air-fuel ratio, the automobile will attempt to stall and idle rough. This symptom often occurs when a vehicle is coming to a stop or braking hard. To fix this, you will need to remove the throttle body assembly and de-carbon it.
2. 1:07 Intake manifold vacuum leak. To fix this, inspect the vacuum hoses and intake manifold gasket. You should check for broken, cracked or disconnected vacuum lines.
3. 1:24 Faulty coil. To fix this you will need to replace the bad coil pack. However, you should test the coil before replacing it. And that means you will need to remove the coil pack from the engine and use a meter to test it.
4. 1:42 Worn, broken or incorrectly gapped spark plugs. To fix this, inspect the each plug and check for a broken insulator, worn electrode and make sure the plug is gapped to factory specifications.
5. 1:59 Spark plug cables crossed or defective. To fix this, make sure the spark plug cables are arranged in the correct firing order and replace any damaged cables.
6. 2:14 Engine idle speed too low. To fix this you will need to check the idle air control valve. A bad idle air control valve can cause a car to idle high, idle low and it can also cause it to stall.
7. 2:32 Air filter clogged. To fix this clean or replace the air filter.
8. 2:39 Leaking head gasket. Most likely your car isn’t running rough because of a blown head gasket. But if you suspect the gasket is blown, you will need to perform a leak down test or use a hydrocarbon sniffer to verify it.
9. 2:58 Worn or burned distributor rotor (if applicable).
10. 3:03 Camshaft lobe(s) worn. For reference, you should not suspect worn lobes unless you have a high-milage car. To know wether or not you have worn lobes, you’ll need to remove the valve cover and measure how far the valve stem depresses into the head as the valve opens and compare that to factory specification wear limits.
11. 3:29 Malfunction in the engine control system or fuel injection system.
12. 3:34 Timing chain or sprockets worn.
And that’s it. These are the most probable causes and corrections if your car idles rough. I hope you found this information helpful. And if you did, hit the thumbs up button.
These service procedures for car idles rough should also be followed for vehicles that:
- rough idle at stop
- what does it mean when your car idles rough
- car idles rough and shakes
- what causes rough idle and hesitation
- car idling rough check engine light
- what causes rough idle at low rpm
- car idles rough in drive
- rough idle at startup
- car idles rough then dies
- car idles rough then shuts off
- car idling rough in park
- car idling rough while stopped
- why is my car idling rough