Rough Idle and Poor Acceleration | DIY Diagnose a Dirty Throttle Body

Rough Idle and Poor Acceleration | DIY Diagnose a Dirty Throttle Body
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Rough Idle and Poor Acceleration

Causes of a Rough Idle or Poor Acceleration?

 

A rough idle is usually caused by your idle fluctuating from a standard idle to a low idle and back. Your tachometer, the gauge on your dash that measures RPMs or the speed at which your engine is cranking.

Poor acceleration is easily defined as lack of acceleration or your car slowly accelerating as the driver presses down on the gas.

Rough Idle and Poor Acceleration – Possible Causes

  • If your throttle body is bad or dirty
  • Bad fuel injectors or a dirty carburetor causing low fuel pressure
  • Mass airflow sensor (MAF) is dirty or malfunctioning
  • A pulley is seized or frozen restricting the serpentine belt
  • You have a vacuum leak
  • The engine air filter is dirty

 

One of the most common causes for a rough idle and poor acceleration is a dirty or bad throttle body.

Locate, Inspect, and Clean the Throttle Body

 

1. Locate the Throttle Body

The easiest way to locate the throttle body on your car is to locate the air filter and follow the air intake hose back to the engine. Since all cars are designed differently, air filter housing and hose designs may vary but the throttle body is usually near the air intake at the engine. If your car has a carburetor, the throttle body will be integrated with the carburetor.

 

2. Is There Carbon Build-Up on the Throttle Body?

Using a flashlight or headlamp, get a good look at the throttle body exterior. Are there dark areas where the hoses connect? This can be a sign of carbon or debris build-up. If carbon and debris build up on your throttle body it will restrict airflow and the function of your throttle body. When you engage the gas pedal the flap in the throttle body should open but the debris and carbon will prevent proper function and may result in a fluctuating idle.

 

3. Check the Throttle Body’s Electrical Connector

Is it clean or does it have discoloration? Is there carbon on it or do you see scorched spots? You can attempt to clean it but if it is very dirty or discolored, it’s usually best to just replace it.

 

4. Throttle Body Removal

The throttle body is attached with a few mounting nuts and bolts as well as a few hoses. Remove all of those before removing the throttle body from your car.

 

5. Closer inspection of the throttle body

Now that the throttle body is out of your car, you can give a good visual inspection for carbon, debris, and other obstacles that may prevent its proper function.

 

6. Throttle Body Cleaning

The best way to clean the throttle body is with choke and throttle body cleaner. This cleaner is a potent degreaser that is used in applications and is highly flammable and is an irritant. Wear gloves and safety goggles since you’re working with chemicals. Even when you spray away from your face, that splashback can get ya. You will find little crevices and crannies that dirt and debris will get stuck in. It is best to use a small soft bristle brush like a toothbrush to do most of the scrubbing on the front of the throttle body. In areas where you find stuck bits, a standard screwdriver can be used but must be done gently. You do not want to score the throttle body. The throttle body shaft is sealed and attached to the interior. You want to reduce the chance of fluid leaking inside so do not tip it up vertically. Keeping the throttle body flat and laying horizontally, you can spray the flap with the throttle body cleaner. Gently scrub the carbon off with the brush. Make sure not to put too much pressure on the flap. It can bend the pivot pins and throw off the calibration. DIY Mechanic’s Note: On a throttle body that is not electronic, you can pull the lever and open the flap. If it is electronic, do open the flap because you may ruin or damage it. Clean the back of the throttle body the best that you can. If you cannot remove all the carbon with light scraping and brushing you can reinstall the throttle body and maybe it will work. If this doesn’t fix the issue, there may be too much carbon built up and the throttle body should be replaced.

 

7. Replace the Throttle Body

Going in the reverse order you used to take it off, reinstall the throttle body, and see if it resolved your issue.


If the problem with a rough idle still exists, buying a whole new throttle body should resolve the issues and Partshawk has the auto parts you need at the best prices online. Contact us for your new throttle body, air filters, hoses, and more.

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