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2009 GMC Sierra 5.3L v8 idles at 3k rpm


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Hey everyone I’m in sort of a pickle 

 

so 2 days ago I help a friend clean out the tb on his 2009 GMC Sierra 5.3l v8 

so we had Down to autozone and ask the guy to see what he recommended he hands us a can of carb cleaner and says this will do, 

get home disconnect the sensor and pull out his tb and spray away 

and boy was it dirty it was thick heavy gunk that’s build up over the years 

so any how we get it cleaned up as much as we could slap it back on 

and once we started it up it idled pretty high like around 3000rpm-3400rpm 

we were told it would do that at first but drive it around for an hour or so and it should adjust we 

gave it a day and still nothing it would still rev high on idles

he calls me and he mentioned that the truck wanted to take off on its own and short after that the truck went into limp mode with a reduce engine power 

he brought it around last night and we checked every thing and replace the sensors on the tb and still nothing 

if anyone has any helpful advise we’d gladly appreciate it

thanks, 

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Hey everyone I’m in sort of a pickle 

 

so 2 days ago I help a friend clean out the tb on his 2009 GMC Sierra 5.3l v8 

so we had Down to autozone and ask the guy to see what he recommended he hands us a can of carb cleaner and says this will do, 

get home disconnect the sensor and pull out his tb and spray away 

and boy was it dirty it was thick heavy gunk that’s build up over the years 

so any how we get it cleaned up as much as we could slap it back on 

and once we started it up it idled pretty high like around 3000rpm-3400rpm 

we were told it would do that at first but drive it around for an hour or so and it should adjust we 

gave it a day and still nothing it would still rev high on idles 

he calls me and he mentioned that the truck wanted to take off on its own and short after that the truck went into limp mode with a reduce engine power 

he brought it around last night and we checked every thing and replace the sensors on the tb and still nothing 

if anyone has any helpful advise we’d gladly appreciate it 

thanks, 

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Have to do a throttle body relearn if by memory serves me correct. The throttle body was use to a certain setting and now it was cleaned and it's saying "I don't know what to do" Hope if you used a brush it wasn't a wire brush.

 

Probably need a bidirectional scanner. Any reputable shop should have this type of scanner if it's halfway decent. Today's vehicles are more complex than prior to 2004 or so and prior.

 

Maybe googling it may give you a different method but I use the tool. If you've got a friend with a fancy scan tool he might be the one to talk to.

 

Stay away from those part's store mechanics.

 

You'll probably get better information over at scannerdanner.com as there's some pretty seasoned guys over there.

 

Here's a method I found on YouTube. Procedure would be similar since you cleaned it.

 

 

#dontbeapartschanger

 

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  • txab changed the title to 2009 GMC 5.3L cleaned Throttle Body, high RPM

The guy at Auto Zone that tossed his two cents in, is that the same guy that could be working at Taco Bell on his days off?  Personally taking advice from someone who more likely less knowledge than his customers since they are attempting to repair their own vehicle. 

 

Spay it some until it is actually clean.  Do not soak any sensors, that stuff hard on sensors.  

 

This will sound stupid, but it will be the best anonymous advice you will get today, don't just ask anyone for advice.  If the guy at "AutoZone" is a real car guy and his card will be parked with pride, and likely cleaned every chance he can.  I am amazed at what they are hiring in these places.  I never applied to work in those stores, always assumed you needed experience.

 

You should be able get it to settle down eventually.  Disconnect the positive cable. get it good and clean.  If you can remove the throttle body off easily, it is best take it off to clean it.

 

Gotta go, my night deliver pizza.

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This is exactly why I never touch the throttle blade when I clean them. I spray them down and use a rag while trying to not push the blade open. Haven't had to do a throttle relearn yet.
Still recommended to do a relearn as when you clean and remove that carbon with the vehicle turned off the carbon is removed as you stated but if you had enough carbon buildup over time the throttle body blade could move incrementally, those small adjustments the video talks about so it's highly recommended to do a relearn regardless. The smallest nuances can make a difference.

I've heard but not tried that there is other methods that work such as removing both battery cables from the battery and holding them together for a small set period of time resets the computer to default settings.

I'll be finding out for sure on the throttle body myself here in the next day or two as I have the upper intake plenum pulled as I had to replace the knock sensors

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I have a tuner and access to a scan tool to perform the relearns, just have never been required to do one.

 

All of the trucks I've dealt with being DBW do not have EGR valves being that GM stopped that in 2001ish on the LS trucks. So the build up of carbon is not that bad at all, they are just oil soaked from the PCV and that gathers dust and dirt to make it bad looking.

 

Throttle learns aren't a bad idea, just haven't needed to do one when I don't open the blade. I'm even 6/6 on my own trucks from a 2006, 2010, two 2012's and two 2016's.

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  • 4 weeks later...
This is exactly why I never touch the throttle blade when I clean them. I spray them down and use a rag while trying to not push the blade open. Haven't had to do a throttle relearn yet.
I touched the blade and used a plastic brush. Hooked battery up after installing it as battery had been unplugged for a couple days as I'd did the knock sensors, upper intake plenum gaskets and cleaned the throttle body. 127,100 miles on it, a 04 Tahoe I'd bought new Jan 15, 2005 and that was the first time it had ever had throttle body cleaned.

Ran great and more power now that the knock sensors were new and intake gasket was replaced.

Next project find the 70, 80 and 84mph vibration while accelerating. Worse @ 70mph under load. All vibrations mentioned are under load.

IF it's not easy I have a new NVH kit from AESwave.com that I'll hook to the 4425 Picoscope and see what kind of wave I get for the vibration and compare to known tech waveform libraries on Autonerdz.com, DN and other groups where there's waveform libraries. Fingers crossed that it's a U-Joint or something like that as I have a couple spares on hand for service calls that'll fit mine as well.

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