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Throttle Body Cleaning & Carbon Removal
Verification, Detection, Removal
Throttle bodies become dirty due to carbon deposits building up in the combustion chamber over time and when the air filter element is still in use well after it has exceeded its recommended service life. Additionally, this condition is worsened if poor quality fuel (non-top tier fuel) or the incorrect fuel is used in the vehicle. Dirty throttle bodies can cause rough engine idle and hamper overall performance. Carbon build-up in combustion chambers form hot spots that can cause pre-ignition and detonation problems. Let’s take a look at how to deal with it.
Verifying A Dirty Throttle Body
One of the most common signs of a dirty throttle body is a rough engine idle. And the best way to verify that is to look at it. Figure 1 shows the top half of the popular 3.6L V6 engine used throughout the FCA US LLC product line. In order to see inside the throttle body, the air intake plumbing must be removed.
First, loosen or remove the band clamp and disconnect the air inlet temperature (AIT) sensor. Pull off the air inlet runner from the throttle body. It is possible to move the air intake runner off to the side to gain access to the throttle bore, but it might be easier to remove the entire air intake runner.
Figure 1 | V6 engine
Second, with the air intake runner removed from the throttle body, take a close look at the bore and the throttle blade (see Figure 2). Most of the dirt will be concentrated in a ring around the edge of the throttle blade with the blade in the closed position. Dirt will also build up on the throttle blade itself.
Figure 2 | Throttle body bore
Detecting Carbon Deposits
The easiest method to detect carbon in the combustion chamber is simply to look inside the cylinder. Obviously, if you remove the cylinder head, you can easily see any buildup of carbon deposits, but that’s not practical unless the engine is being serviced for something like a head gasket.
Remove the spark plug and check for carbon deposits on it. Next, take a look inside the combustion chamber through the spark plug hole. This is not as easy as it sounds. If the piston is at top dead center (TDC) and you get your head at a good vantage point (difficult to do on late model cars), you might be able to see deposits on the piston by shining a flashlight through the hole.
Alternatively, use a portable camera. This is similar to using a boroscope, but a bit more sophisticated. It looks similar to a pocket digital camera except it has a long, thin tube with a camera probe on the end which easily fits through a spark plug hole. Also, fiber optic cameras are available for use with smartphones. Either device will allow you to look inside the combustion chamber to determine if heavy carbon deposits are present.
If the carbon deposits are significant, engine misfires can become a problem. What to look for:
- This condition is usually more noticeable during cruising speeds and heavy engine load conditions.
- Misfires are more likely to occur in all cylinders instead of only one cylinder.
- Misfires will store a diagnostic trouble code (DTC) in the memory of the PCM and will illuminate the MIL or check engine light.
- The DTC that will be read on your scan tool will be P0301-# where # is the cylinder number.
Cleaning & Removing Dirt and Carbon
Mopar has a wonderful product to use for removing carbon deposits – Mopar Combustion Chamber Cleaner P/N 04318001AE (see Figure 3). With the air intake runner removed and the engine running, spray the cleaner directly into the throttle body bore. The cleaner will be distributed to each cylinder. Spraying the cleaner into the throttle body will also clean the throttle body, so doing both cleaning jobs with one step.
Figure 3 | Cleaner
While spraying the cleaner into the throttle body, move the spray around the bore to remove that ring of dirt around the blade. Also, spray cleaner directly onto the throttle blade to clean it.
Note: It will probably be necessary to increase engine speed slightly to keep the engine running at a constant speed; this can be done with the throttle lever, or if the vehicle is equipped with a drive-by-wire throttle, you’ll need an assistant inside the car to press the accelerator.
To maximize your cleaning efforts, spray the cleaner into a small bowl until it’s filled with liquid cleaner. With the engine running, remove the vacuum hose closest to the throttle body and place the end of it into the bowl. The engine vacuum will suck the liquid cleaner into the intake manifold. This trick will ingest more cleaner into the intake system than spraying it and will clean the combustion chambers quicker. Repeat as necessary.
After the cleaning procedure is done, reconnect the air inlet runner. Erase the DTCs with the appropriate scan tool. Test drive the vehicle in accordance with the Freeze Frame data. With the scan tool, view the Misfire Monitor. If no DTC is stored, the cleaning job was a success.