DIY Throttle Body Cleaning

This is an easy cleaning DIY that will likely improve the feel of your S65's throttle response and may reduce stress on your car's throttle actuators which may extend their operating lifespan. If you can change your car's oil, you can complete this DIY.

Examples of the problem. Check out the carbon build up on these S65 throttle bodies (engine was throwing codes):

This one was not as dirty, but was also throwing codes at the time of filming:

This one had decent buildup and possibly some sort of TA related issue as well:

Hand Tools Needed:
T25 Torx bit (for air box removal)
10mm socket (for 2 coolant reservoir bolts, 2 for the air box removal)
6mm socket (for 8 throttle body clamps)
socket wrench
extensions (I used 6" and 9", other sizes can work also)
a small brush (old tooth brush or I used this phosphor bronze brush for gun cleaning and found it to be very effective, image borrowed from here)


Materials Needed:
shop rags or paper towels
throttle body cleaner (image link borrowed from here)


Step 1: Remove the plenum (for novices, its the big plastic thing on top of your engine with the MV8 logo). Follow the instructions in these great DIYs to learn how to do this:

a. W///'s DIY with lots of pictures.
b. elp_jc's DIY instructions (no pictures anymore, but well written and concise instructions).
c. Rat3d///M's DIY with plenty of pictures.
d. Atruelunatic's DIY with lots of pictures.
e. Ovalbore's.

Once you have the plenum off you may see something similar to this and say to yourself, looks good, what's the problem?


However upon closer inspection you may see this or worse:


Perhaps for an engine that doesn't have a history of throttle actuator issues this wouldn't be a big deal, but this is an S65. The buildup around the hinges is of particular interest. This buildup at the hinges creates some resistance that that over time will require more force from the actuators to turn, particularly at the least used condition, full throttle.


Step 2: One at a time clean the throttle bodies by spraying the throttle body cleaner on them, using your brush to agitate the buildup and then use a shop rag or paper towels to clean up the gunk. When you open the valves to clean the hinges and the area just below the valves to try place a shop rag or paper towel below the area you are cleaning to catch the oil, cleaner and gunk.

Here is one throttle body cleaned (lower one) and one still dirty (upper one).


Step 3:

Re-install the plenum.

The first time I did this I was not careful and allowed too much cleaner (and carbon gunk) to into the intake. The car ran terrible for several minutes as the gunk and throttle body cleaner I didn't catch was burned off by the engine. This of course fouled up the pre-cat O2 sensor a left me with a check engine light, error code 0027C5. I replaced the pre-cat O2 sensors and the check engine light is now gone. I was much more careful for subsequent cleanings and did not foul up any O2 sensors. If your car is catless this concern may be mute.

Similar to previous cars I've completed this service for, the M3 feels like it has a mild increase in throttle response speed afterwards.

If you want to change out your pre-cat O2 sensors or spark plugs to possibly further improve responsiveness, check out these guides:

O2 pre-cat sensor DIY guides:
a. DIY here from DAT240.
b. DIY tips here from Brian_Fantana.

Spark plug change DIY guides:
a. DIY here by Kartelli with recent posts and tips from members.
b. DIY by Sean05 with lots of photos here).

Edit: If you would like to take the extra time to fully remove the throttle bodies before cleaning them, check out this link here where a guy did just that on his S85, which should be very similar to the procedure on the S65 motor.

So let me just sum up. The diy calls for cleaning the itb butterfly hinges on the car, in order to maybe potentially avoid more stress on the actuators, but will almost definitely cause o2 sensor failure and may foul the plugs too, the plugs which are the means by which all knock detection is accomplished on this emgine? Is that the gist?

Pull the tb's off the car for god's sake if you're going to attempt this.

Richbot wrote

So let me just sum up. The diy calls for cleaning the itb butterfly hinges on the car, in order to maybe potentially avoid more stress on the actuators, but will almost definitely cause o2 sensor failure and may foul the plugs too, the plugs which are the means by which all knock detection is accomplished on this emgine? Is that the gist?

Pull the tb's off the car for god's sake if you're going to attempt this.

Completely unnecessary. Link added above for those who want to do that.

I believe someone had done a diy on the e46 and he pulled the throttle body rack.

It's obviously twice the work to pull two racks on the v8 and man some of those 10mm nuts are a complete bitch. I feel like I'm doing surgery trying to line up those nuts to put them back in. And this was with the motor on a stand, not in the car.

I'd also recommend using some sort of lube like motorcycle chain grease to keep em nice and smooth.

Thanks for the diy!

why would this method cause O2 sensor failure or foul plug ? throttle body cleaners are used all the time on all cars without issues. why would it in this case ?

thanks for taking the time to contribute to the forum.

however, i'm with Richbot- if i was going this far, i would just go the extra mile and take them off and really scrub them.

roastbeef wrote

thanks for taking the time to contribute to the forum.

however, i'm with Richbot- if i was going this far, i would just go the extra mile and take them off and really scrub them.

Yeah what he said sorry if I was a little too Internet-jerky

Done this on many cars over the years.

Don't douse down into the throttle bodies. I understand using the fluid to remove the black carbon build up makes sense. But what your doing is pushing the carbon build up into the heads themselves. This causes idling issues which he explained and adds contaminants to your oil.

So grab a rag and open the plates by hand and clean each plate. At the tight spots use a Q-tip. Spray throttle body cleaner on the q-tip and rag and clean as you go along.

If you want to do a full cleaning, remove them completely and while you are add it...i would half shaft each body for some performance gains.

Harrry wrote

Done this on many cars over the years.

Don't douse down into the throttle bodies. I understand using the fluid to remove the black carbon build up makes sense. But what your doing is pushing the carbon build up into the heads themselves. This causes idling issues which he explained and adds contaminants to your oil.

So grab a rag and open the plates by hand and clean each plate. At the tight spots use a Q-tip. Spray throttle body cleaner on the q-tip and rag and clean as you go along.

If you want to do a full cleaning, remove them completely and while you are add it...i would half shaft each body for some performance gains.

Should probably just turn them into slide throttles "while we're in there"

Mines since my engine is on the rebuild side. Before and after

This is the worst DIY I’ve seen in awhile.