Why you may need to clean a 4.2L I6 Throttle Body

Busterbrown

Member
Dec 4, 2011
253
An obvious end-result to a clean throttle body is a smooth idle. Perception may have you believe in stronger, more lively acceleration. Unfortunately, any significant amount of opening of the throttle plate washes away those claims. Remember to disconnect your battery for the relearn to take place.
 

Busterbrown

Member
Dec 4, 2011
253
trailblazer075 said:
Thank you!
The consumption is lower or it there is no change?
As far as fuel consumption, I would say at best, negligible.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I'm going to change the title of this thread to make sure folks don't come here looking for a How-To thread.

The main trouble symptom is an engine whose idle goes up and down as the AC compressor cycles on and off, often every 15-30 seconds. The AC compressor cycles on and off even when you don't think it needs to at 35-40 degrees F or 2-5 degrees C, because the designers wanted the cabin to be dehumidified to keep the windows clear for safety.

The idle can go from 400-900 RPM when the desired RPM is a steady 600. Sometimes the low side can go under 400, and then the engine can stall, or the oil pressure goes so low that the switch tells the PCM that the oil pressure has been lost and then if you have a DIC it will say "Oil Pressure Low Stop Engine".

If you turn the AC compressor off by pressing the snowflake button, and the idle gets better (if you're in a normal mode and not in recirculate mode), then that's almost always a dirty throttle body.

It can also happen that your idle is OK, then you discharge or change your battery, and the PCM forgets how to handle a dirty throttle body. Then when you charge or change your battery the PCM attempts to relearn the dirty throttle body and it fails, and the idle becomes variable.

The root cause is that the GM designers were cheap, failed to install a normal PCV valve, and the back of the throttle body gets full of sticky gunk from crankcase blowby.
 

Busterbrown

Member
Dec 4, 2011
253
the roadie said:
I'm going to change the title of this thread to make sure folks don't come here looking for a How-To thread.

I was thinking of requesting the same thing. :thumbsup:
 

trailblazer075

Original poster
Member
Dec 17, 2011
323
LAGNY SUR MARNE FRANCE
Hi all!
J have made ​​the job of cleaning!
fairly easy
J have been afraid to return because when the engine started, it did not exceed 3000 rpm munites!
I disconnected the battery yet!
So I j turns off the engine to store my tools a little.
I went to tour the neighborhood and the engine returned to normal.
At idle it runs slower I am currently at 600 rpm in park position.
Here are the before and after pictures.
I could not rub it 100% because I had no one toothbrush to avoid damaging the part.
front
back

front clean

back clean

Thanks for your help!
I m make in to 20/25 minutes:thumbsup:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
trailblazer075 said:
J have been afraid to return because when the engine started, it did not exceed 3000 rpm munites!
This is normal in PARK or NEUTRAL. It is a RPM limiter put there by the designers because there is no good reason to push the engine to high RPM like that except as a test. But they don't care about the owner's doing the test. They worry about dumb owners getting the RPM high in NEUTRAL, then shifting to DRIVE, attempting to make the tires go chirp, and breaking the transmission from the abuse.
At idle it runs slower I am currently at 600 rpm in park position.
600 RPM is the perfect number.
 

ChevyIIfan

Member
Dec 18, 2011
2,127
Thanks for the info Roadie. I've seen the threads about how to clean the throttle body, but have never seen a breakdown of the symptoms indicating a throttle body cleaning is needed. Mine is still new enough that I haven't needed one yet, but I will definitely be marking this one for future reference. :cool:
 

woody79

Member
Dec 3, 2011
351
I've been thinking of taking a look at my TB to see what shape its in. My truck is a '08 with 78,000. We got it with around 50,000 on it.

I know it may sound like a stupid question, but do all years of our Trailblazer's suffer from dirty TB's? I'm guessing so as Roadie said GM were cheap and didn't install PCV valve's.

Edit: Also, thanks Roadie for the break down on why its important to clean the TB and what symptoms to look out for. I'm sure a lot of people will find this thread useful.
 

ChevyIIfan

Member
Dec 18, 2011
2,127
woody79 said:
I've been thinking of taking a look at my TB to see what shape its in. My truck is a '08 with 78,000. We got it with around 50,000 on it.

I know it may sound like a stupid question, but do all years of our Trailblazer's suffer from dirty TB's? I'm guessing so as Roadie said GM were cheap and didn't install PCV valve's.

Edit: Also, thanks Roadie for the break down on why its important to clean the TB and what symptoms to look out for. I'm sure a lot of people will find this thread useful.

This comment is merely my jaw droppoing. 78k on your '08??? I have 30,500 on my '08..... :crazy: Best of luck cleaning yours!
 

MichEnvoyGuy

Member
Dec 3, 2011
522
woody79 said:
I've been thinking of taking a look at my TB to see what shape its in. My truck is a '08 with 78,000. We got it with around 50,000 on it.

I know it may sound like a stupid question, but do all years of our Trailblazer's suffer from dirty TB's? I'm guessing so as Roadie said GM were cheap and didn't install PCV valve's.

Edit: Also, thanks Roadie for the break down on why its important to clean the TB and what symptoms to look out for. I'm sure a lot of people will find this thread useful.

I just cleaned my 2002 Envoy's TB last year and at that time it had about 135,000 miles on it. I wasnt experiencing any driveability problems, I merely did it because I was bored one day.

Mine wasnt bad at all. It had some build up on the back side of the throttle plate but it in no way interfered with the performance of it. I cleaned it up with some seafoam spray and a toothbrush and put it back on. It must've been fine to begin with because I didnt disconnect my battery to do a relearn and it never gave me any problems.
 

v7guy

Member
Dec 4, 2011
298
as mentioned previously, I experienced an irratic idle, a dip in rpms as the compressor kicked on and off, and on a few occasions it stalled. Cleaning the throttle body solved all these issues.
 

woody79

Member
Dec 3, 2011
351
ChevyIIfan said:
This comment is merely my jaw droppoing. 78k on your '08??? I have 30,500 on my '08..... :crazy: Best of luck cleaning yours!

:biggrin:

When we got our TB back on Nov of '09, it had about 50k on it. So we've put about 20k on it in 2 years.

:offtopic:
 

trailblazer075

Original poster
Member
Dec 17, 2011
323
LAGNY SUR MARNE FRANCE
To be honest with you, mine too had no problems but finally I saw the dirt well to do so.
I am sure that in 10 years this has never been done!
The only problem that I've had with my truck have spark plugs and ignition coils that I have had to replace because there were only five-cylinder operation.
 

Menthol

Member
Dec 8, 2011
177
trailblazer075 said:
To be honest with you, mine too had no problems but finally I saw the dirt well to do so.
I am sure that in 10 years this has never been done!
The only problem that I've had with my truck have spark plugs and ignition coils that I have had to replace because there were only five-cylinder operation.

Are you sure that's ONLY 10yrs of not being cleaned lol :biggrin: Man, that was really a lot of carbon buildup.
 

berto1014

Member
Dec 25, 2011
12
Haha or you can have symptoms like me where you engine will be idling perfectly fine at 600 rpms, then just shut off with no stutter in the idle and will tell you low oil pressure. Apparently this means, "clean throttle body".
 

miron

Member
Dec 29, 2011
56
It appears I will need to clean my TB on my '06 Envoy w/ 117k mi. When it's cool outside, sitting at a light idle, the RPM will periodically drop to around 500RPM and my charging system will drop from 14VDC to 11.5 and the dash lights will dim. Annoying! So now I have a good idea of the issue. This has been going on for a couple of years now. I used to have to drive 20mi round-trip to work and home every day. Did this for eight months so I am pretty sure it contributed to the fouling of the TB. As soon as it warm up a little (I have no garage (sniffle)) I'll do the job, take pics, and let ya'll know the outcome. Wish me luck! Oh, and Happy New Year to you all!
 

christo829

Member
Dec 7, 2011
508
Fairfax, Virginia
trailblazer075 said:
I must say that since the cleaning of the BODY, my check engine light no longer illuminates.
Yet this is not related?:undecided:

Could have been related, but hard to tell without knowing what the code was that was causing the light.

The dirty throttle body could have been affecting your air/fuel mixture, making it run a bit rich, which will throw
a code, or the code could have been reflecting a throttle position sensor issue. There are probably plenty of other
possibilities, but those are a couple just off the top.

Cheers-

Chris
 

LennieM

Member
Jan 2, 2012
28
I cant find any throttle body cleaner in any stores where i live, is it possible to use brakecleaner or carburator cleaner?
 

christo829

Member
Dec 7, 2011
508
Fairfax, Virginia
LennieM said:
I cant find any throttle body cleaner in any stores where i live, is it possible to use brakecleaner or carburator cleaner?

If the carb cleaner says someplace on it that it's "sensor safe", you can use that. Some carb cleaners (and some formulations of Brakleen) can
melt plastics, so you definitely want to avoid that. I have a screwdriver with a custom grip thanks to that... :wink:

Cheers-

Chris
 

Mark20

Member
Dec 6, 2011
1,630
As a side note I was having some idle problems. RPM would drop and the engine would catch itself. Over Christmas I cleaned the throttle body, the back of the air plate was completely black. No idle problems since then. Hardest part of the job was getting the air intake off the resonator on top of the engine. At 65k miles it was just stuck on. Ended up taking the air cleaner housing apart so I could get enough wiggle on it.

Sent from my Xoom using Tapatalk
 

LennieM

Member
Jan 2, 2012
28
ok ill try with wd40 then, expect my throttlebody to be very dirty since i have never done this i my 70000km and if this is not something they do on any service then i doubt the previous owner has done this. that would be 230000kms without cleaning :smile:
 

miron

Member
Dec 29, 2011
56
miron said:
It appears I will need to clean my TB on my '06 Envoy w/ 117k mi. When it's cool outside, sitting at a light idle, the RPM will periodically drop to around 500RPM and my charging system will drop from 14VDC to 11.5 and the dash lights will dim. Annoying! So now I have a good idea of the issue. This has been going on for a couple of years now. I used to have to drive 20mi round-trip to work and home every day. Did this for eight months so I am pretty sure it contributed to the fouling of the TB. As soon as it warm up a little (I have no garage (sniffle)) I'll do the job, take pics, and let ya'll know the outcome. Wish me luck! Oh, and Happy New Year to you all!

Well I did it an what a difference a little cleaning makes! No more lag in my idle and the RPMs stay at about 540 in drive while stopped. After 120K it was pretty dirty. Alot of varnishing and crud. Took all of about 30 min to complete. The only investment was time and a $4 can of carb cleaner. Over the years ya'll have saved me a fortune, much frustration, and bloody knuckles! Thanks! :wootwoot::wootwoot:
 

sevendj

Member
Dec 9, 2011
52
the roadie said:
They worry about dumb owners getting the RPM high in NEUTRAL, then shifting to DRIVE, attempting to make the tires go chirp, and breaking the transmission from the abuse. 600 RPM is the perfect number.

But it's so much fun to do to a rental!


On a side note... looking at my butterfly valve without removing it from the engine, it looks slightly dirty around the top edge, but generally pretty clean. Is it the interior side of the butterfly that gets dirtier?

I'm at 70k and in need of changing my air check valve anyways... I was going to throw the TB cleaning into the mix, but hesitated when I saw such a clean butterfly valve - but now looking at these pictures, it appears that the exterior side is cleaner anyways. Perhaps I'll take it off to look.
 

400Magnum

Member
Dec 23, 2011
49
the roadie said:
The root cause is that the GM designers were cheap, failed to install a normal PCV valve, and the back of the throttle body gets full of sticky gunk from crankcase blowby.

Roadie, while you usually give very good technical advise, I have to take exception to your comment about designers. As a former designer at GM, I can tell you that the designers have very little to do with the parts being selected, they are on a short leash from the engineer, who are in turn on a short leash from the program managers, who are on a short leash from the accounting department. The people that control the money have the lion's share of control over how an engine is designed and what can and can't be done.

I just want to set the record straight. Thank you.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
400Magnum said:
Roadie, while you usually give very good technical advise, I have to take exception to your comment about designers. As a former designer at GM, I can tell you that the designers have very little to do with the parts being selected, they are on a short leash from the engineer, who are in turn on a short leash from the program managers, who are on a short leash from the accounting department. The people that control the money have the lion's share of control over how an engine is designed and what can and can't be done.

I just want to set the record straight. Thank you.
Oh my goodness, I totally agree. :yes: Having a 38 year career in electronic system design and support, I've seen it all from the engineer's point of view, with a few years in management where I saw more of the bigger economic picture. I'm guilty of falling back into some stereotypical shorthand in that post you pointed out, and I certainly meant to lay ultimate blame on the management chain who ultimately have to answer to the shareholders. Customers and employees are only two of the three legs that support any public corporation.

I wrote my "16 rules" manifesto with this exact concept as Rule #2 of troubleshooting:

2. Never give up, unless forced to by economics.
There are no mysteries unless you give up. Everything has a root cause. It may not be economic to run all possible tests to
discover the ultimate root cause, but problems can and do have a solution, even if it’s a compromise. Throwing out,
discarding, or recycling an item because it can’t be fixed is ultimately an economic decision, not a technical one. A corollary
is that designers who design items to not be maintained easily are under orders from bad management, who should take
the blame for being bad world citizens
.


For more reading:

www.roadie.org/bill carton's 16 rules .pdf
 

400Magnum

Member
Dec 23, 2011
49
I understand, I think we are all guilty at one point or another of being quick to use the generic thought of designer = solely responsible for the products outcome.

I apologize for my response, because it's a sore spot with me. I have a mother-in-law who is quick to blame the engineers for everything and has no idea what is involved with products reaching the public, despite repeated attempts to explain to her.

I started my career as an engineer and as jobs got scarce, I had to change gears and landed a job as a designer in order to pay the bills. Oddly enough, one of the reasons they hired me as a designer was because of my "engineering degree and expertise" and they wanted input during the design process. However, shortly into my first design project, I was told by my supervisor that "I wasn't paid to think, I was paid to follow instructions." Since everyone held this guy in such high regard as a leader, I complied and kept my mouth shut for the next two years until I could find another job that actually wanted ideas from the designers.

Thanks for understanding my point and I agree with your Rule #2. I'm intrigued and will have to take some time to read the rest of your manifesto. :thumbsup:

Now, back to the subject at hand. I am going to be installing a tuned PCM soon, and I know I need to clean the TB as well because I also have the wondering idle problem that is getting more pronounced and bothersome. I was wondering about a revising the cleaning procedure. I noticed that Seafoam now makes an aerosol version of their solvent that everyone likes to suck into the intake via the brake vacuum tube. I was wondering how it would be to pull the resonator off the TB, start the engine, and spray the Seafoam into the TB while the engine is running, give it a couple of quick jabs to get it off idle every now and then while spraying. Wouldn't the aerosol do a better job of covering the inside of the intake? Once the exhaust starts clouding up, shut the car off and let it soak for a few minutes while the TB is removed and cleaned thoroughly. Reinstall the TB, start 'er up and let the smoke show continue. I just think the aerosol is going to do a better job of fogging the inside of the intake to clean it and may be enough to clean the TB without having to even remove it.

Thoughts??
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
400Magnum said:
... I was wondering about a revising the cleaning procedure. ...
You can try, but the procedure was proven by years of success at trailvoy. The back of the throttle body usually looks like a Dodge City spittoon after 30 years of use in the 1800's, which was then put away in a museum, uncleaned, and dried out for the next hundred years. The cleaning process isn't that bad, but you have to take it off and get on the backside and around the knife-edge of the butterfly disk where the sticky buildup interferes with smooth operation. The center of the back of the disk always looks bad, but never needs cleaning like the rest, because it's not interfering. I don't think it would surprise anybody to hear that I don't even bother with the center of the back of the disk. Saves me a minute per cleaning. But I like leaving dirt in hidden places because it bothers the OCD members to read that. :raspberry:
 
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miron

Member
Dec 29, 2011
56
Based on my recent experience in cleaning my Envoy's TB (Last Saturday), I would recommend taking it off and cleaning it thouroughly. Much of the carbon/gunk/varnish can not be removed by merely spraying a cleaning solvent into the running engine. It took me a good 15 minutes of solvent soaking and brush scrubbing to get it all off. Specifically the interior side of the butterfly. It was quite varnished and required much attention. It is not a difficult procedure at all and I thank those that post the step-by-steps. My performance has increased dramatically and my idle is now where it should be. I used a Gumout carb cleaner product ($4) and one large can was more than enough. One point to note, despite the posted procedure, I did not have to remove the air box on my 6cyl.

I just have a question as to design vs cost. Isn't the PCV considered intregal to performance/operation? Would cost REALLY be the reason for omisson of a semi-vital and proven part?
 

400Magnum

Member
Dec 23, 2011
49
I've had the TB off several times already, so I do realize just how cruddy the back side of the throttle blade gets. Roadie's description is pretty accurate.:rotfl:

I guess my main thought was the aerosol would do a better job of getting over the entire surface of the inside of the intake manifold, rather than trying to suck up a liquid and have larger droplets trying to coat everything. Maybe a combination of both to do a really good job cleaning the manifold?? Hit it first with the can of Seafoam to get the major crud soaking and removed, then hit it with the spray to fog the entire inside of the intake. I dont know, maybe it's way overkill for minimal, if any, gain. It was just a thought. I'll probably just stick to the tried and proven procedure and save myself a few bucks for now, then when money isn't so tight I might try the spray on a more frequent interval to keep things cleaned up.

Thanks for the thoughts guys!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
miron said:
Would cost REALLY be the reason for omisson of a semi-vital and proven part?
Yes, ESPECIALLY if the dealers benefit by overcharging for throttle body cleaning and even REPLACEMENT, which is how we've read some owners were abused over the years when they reported erratic idle. There are many items that could have been easily designed for better maintainability, but were not, either due to schedule/economic pressure in the design process or a motivation to throw the dealers a bone by letting them charge more labor hours for long term maintenance. Upper control arm bolts hitting the body sheet metal because nobody checked for interference. HVAC actuators. Thermostat. Spare tire winch. Motor mounts. The list goes on.
 

miron

Member
Dec 29, 2011
56
Good point Roadie. It's a vicious circle and revolves around making a buck or saving a buck. The consumer suffers the concequences.:crazy:
 

sevendj

Member
Dec 9, 2011
52
Consumer education is one of the most important parts of protecting ourselves in the free market. Unfortunately, so often it is up to the consumer to seek out the information that protects them from these situations.
 

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