Successful Throttle Body Cleaning

[HomerTHX1138]

My 93 LS400 139K would hesisitate at low throttle from the line. It would also dive in idle RPMs when the AC was turned off or the car put in park. It also shudders at ~45MPH, and has a vibration and noise when in overdrive or very low RPMs while driving. (the last problem I knew would not be addressed by the T.B.C. and was not)

I posted a thread about it and got many suggestions. Today I replaced the air filter and cleaned the throttle body. The result is low throttle acceleration is now smooth and the idle does not dive when the AC is turned on or off or the car is put into park.

The album only let me put one photo in so here's the before:

It was NASTY. The carbon would come off in thick black crusty shiny spots and a ton of brown residue.

BTW, the air filter looked clean but DUH I was looking at the backside when I first opened the plenum. The front side was a study in airborne bugs. All kinds of shiny insects were crammed in - at least 50, along with dust dirt etc.. .

I have more photos on the cleaning process / filter comparision (including the one in the engine and the Japanese brand I put in side-by-side), and the after cleaning.

Note that my throttle body had ONE butterfly valve. The instructions show two but my 93 has one.

Also I would suggest that people performing this plug the first hole with a rag. The second, rearmost hole has a lip around it to prevent stuff from draining into it and I believe the whole assembly has a slight tilt toward the opening of the body. Therefore, spraying the cleaner causes it to run toward that first hole. I also found that a hanger with the cardboard tube proved to be perfect for a tool: The cardboard tube could be used to push rags into the TB and the coat hanger, straightened but with the hook left at the end, was a safe way to retrieve rags from inside the body.

The valve and area around the valve are now clean. However, there is still build up back in the plenum. I found it impossible to make the whole "box" clean from that orifice and I spent about 1.5 hours on the actual cleaning part. Basically, you have to draw the line somewhere and frankly I wasn't sure where some of the gunk in the rear of the TB would run to if I managed to loosen it as I believe the box then extends right and left when looking into the TB.

That's about it. Bosch Fuel filter comes next. I also bought Jap distributor rotors and caps but found out that

my grandmother had these replaced with the seal and timing belt job done less than a year ago.

Thanks to Curt for his excellent how-to here:

http://www.lextreme.com/tb.htm

[harjp]

Hey, this is great! I'm bored and looking for something to do, so this is it!

And the website on which this how-to is located has all sorts of other great stuff.

Thanks!

[TexasLexus94]

Wow, I'm surprised your throttle body was so dirty. I cleaned my 94LS with 105 k with a toothbrush and carb cleaner, and while it was lightly sooty, there were bugs or other such junk in the body. Just wondering why there would be so much detritus in the system. Maybe it's a result of where you live? I live in Las Vegas, where nothing lives without water and shade, so bugs are not a problem.

[harjp]

Here's another how-to on cleaning the throttle body.

http://www.lexls.com/tutorials/EFI/throttlebody.html

This one shows how to remove it completely, which means draining the coolant. But if mine's as dirty as Homer's, I'd like to be able to clean it without worrying what's getting into the air intake chamber. I'll also be able to wipe out the air intake chamber some.

The one thing I won't do is use a screwdriver to scrape the throttle plate!

[AussiLS400]

The LEXLS article is a good way of doing this although i found a couple of shortcuts. I found that the coolant loss amounted to about a thimble full when disconected. Hardly worth dropping the whole lot out. Also i found i could get the throttle body off without taking the air cleaner and related off. Just a quick note when cleaning poke some wire down the three pipes on top to clear any carbon buildup in these.

[harjp]

The LEXLS article is a good way of doing this although i found a couple of shortcuts. I found that the coolant loss amounted to about a thimble full when disconected. Hardly worth dropping the whole lot out. Also i found i could get the throttle body off without taking the air cleaner and related off. Just a quick note when cleaning poke some wire down the three pipes on top to clear any carbon buildup in these.

Thanks for posting this.

I read what's involved in draining the coolant and its kind of a PITA. I was thinking of disconnecting the coolant hose anyway since it's so high up in the system. Now I know that will be OK.

Also, it sounds as if you were able to do this while leaving the mass air sensor in place. That's good to know as well.

[HomerTHX1138]

TexasLexus,

My post was a bit confusing. The throttle body was absoutely coated in black gunk. I know for a fact that premium was not run in the car the last few years but I don't know if this contributes to the build up. ANyway, the bugs were on the air filter face.