Rough Idle? Weak Acceleration? How to Diagnose and Clean a Throttle Body

If your car, truck, or SUV has a rough idle and is slow to accelerate, there may be a problem with the throttle body. Our experts in this article and video explain how to inspect and clean a throttle body and review other potential causes of weak acceleration and a rough idle.

Causes and Fixes for a Rough Idle and Weak Acceleration

What Causes a Rough Idle or Weak Acceleration?

A rough idle happens when the RPMs or the engine speed tends to fluctuate erratically.

Weak acceleration or slow acceleration happens when the vehicle is slow to pick up speed or accelerate when the driver presses the gas pedal.

Potential Causes of Rough Idle and Weak Acceleration

A common cause for a rough idle and weak acceleration is a dirty or bad throttle body.

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How to Inspect and Clean a Throttle Body

Steps for Inspecting and Cleaning a Throttle Body

How to Inspect and Clean a Throttle Body

  1. Find the Throttle Body

    Find the air filter and trace the air intake tube to the engine. Not all cars are designed the same, but generally the throttle body is closest the engine where the intake meets the engine, between the air inlet and the air intake.

    Cars with carburetors have the throttle body integrated in with the carburetor

  2. Inspect the Throttle Body for Carbon Build-Up

    Get a clear view of the outside of the throttle body. Look for dark areas where the hose connects to the throttle body, like dark carbon or debris, which can cause a restriction in air flow and cause a delay. As the flap opens when the pedal is pressed, if it’s blocked by debris or carbon, it will cause a delay or erratic idle

  3. Check the Condition of the Throttle Body’s Electrical Connector

    Disconnect the electrical connector. Check the electrical areas for discoloration or corrosion and clean it or replace the connector.

  4. Remove the Throttle Body

    Remove the throttle body by removing the mounting nuts and a few hoses that attach to it

  5. Inspect the Throttle Body Further for Carbon Build-Up

    Check both sides of the throttle body for carbon build-up

  6. Clean the Throttle Body

    Clean the throttle body with a carb choke and throttle body cleaner.

    Wear hand and eye protection since you’re dealing with chemicals.

    Clean the front area with a soft bristle brush. A flat blade screwdriver may help remove stuck bits, but it should not be used to scrape off carbon and scrape the throttle body.

    The shaft will be attached to an interior area, and it is sealed, but to reduce the chance of fluid leaking inside, do not tip the throttle body vertically.

    Hold the throttle body flat and horizontal and spray the flap. Clean off the carbon with a brush. Do not push the flap too hard since that can mess up the calibration.

    If the throttle body is not electronic, you can pull the lever and open it up, but if it is electronic, do open the flap. Clean the back of the throttle body. You may not be able to remove all carbon with light scraping and cleaning. You can try to reinstall and maybe it will work. If it doesn’t, there is probably too much carbon and it will need to be replaced.

  7. Replace the Throttle Body

    If slow acceleration and a rough idle persists after cleaning the throttle body, a new or clean throttle body should fix this problem.

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Rough Idle? Weak Acceleration? How to Diagnose and Clean a Throttle Body
Article Name
Rough Idle? Weak Acceleration? How to Diagnose and Clean a Throttle Body
Learn the common causes of a rough idle and weak acceleration including how to diagnose and clean a throttle body.
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1A Auto
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