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#4513926 - 09/12/17 06:44 AM GMC Envoy Rough Idle
carguy996 Offline


Registered: 10/26/06
Posts: 260
Loc: Illinois
I have recently purchased a 1 owner 2005 GMC Envoy with the 4.2 I6 motor to pull my camper. The vehicle has 97,000 miles and overall in decent shape, needs some TLC here and there but ill get it waxed this weekend and looking good. What I did notice is when it idle its a little rough and unsteady. When I accelerate it hesitates just a second and then it runs perfectly and smooth until I stop and it has to idle. Later this week I plan to do an oil/filter change, spark plugs and clean the throttle body. I also plan to run some SeaFoam through the gas and replace the air filter. This vehicle hasn't been used much recently by the previous owner so it has been sitting for a few months.

Anything I am missing here? I am assuming my issue is the plugs and throttle body. The car has no codes according to my reader and no warning lights.
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#4513931 - 09/12/17 06:54 AM Re: GMC Envoy Rough Idle [Re: carguy996]
FordBroncoVWJeta Offline


Registered: 04/16/16
Posts: 769
Loc: KS
My step dad just purchased a 2007 Trailblazer with the I6. They are smooth as silk. I have also worked on a ton of them at Walmart. They will last a very long time. It sounds like maybe bad plugs, MAF senor, gas filter, sometimes even a 02 sensor.
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#4513976 - 09/12/17 07:50 AM Re: GMC Envoy Rough Idle [Re: FordBroncoVWJeta]
carguy996 Offline


Registered: 10/26/06
Posts: 260
Loc: Illinois
Thank you! Great to know they are reliable vehicles and will go a while! Doesn't look like the MAF sensor is very expensive so ill grab one of those as well.
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#4513982 - 09/12/17 07:55 AM Re: GMC Envoy Rough Idle [Re: carguy996]
WobblyElvis Online   content


Registered: 09/23/14
Posts: 1346
Loc: Toronto Canada
You could save some money and just clean the MAF sensor.

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#4514041 - 09/12/17 08:47 AM Re: GMC Envoy Rough Idle [Re: WobblyElvis]
Bgallagher Offline


Registered: 04/17/12
Posts: 3159
Loc: Boston, MA
Originally Posted By: WobblyElvis
You could save some money and just clean the MAF sensor.


+1 MAF sensor is my first thought. While you are in there I would check out the throttle body and the air filter to make sure they are in good shape. Clean/replace if needed. Sounds like the Envoy is lacking air. If none of that works I would check out the 02s to see if they are running lazy.
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#4514079 - 09/12/17 09:24 AM Re: GMC Envoy Rough Idle [Re: carguy996]
FordBroncoVWJeta Offline


Registered: 04/16/16
Posts: 769
Loc: KS
I would not recommend cleaning a MAF sensor. Many people do but nothing will be better than a brand new one. And they a cheap. Amazon has an ACDelco for $47. Also if you are going to replace an 02 Sensor you will only need the upstream sensor (About $40), since the downstream sensor is purely for emissions.(Just turns the check engine light on if the catalytic converter isnt doing its job.)
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#4514090 - 09/12/17 09:39 AM Re: GMC Envoy Rough Idle [Re: carguy996]
Lignums Offline


Registered: 11/25/16
Posts: 21
Loc: Ohio
Check for spark, coils and plugs. Replace the fuel filter immediately if possible. I believe the 2005 model still has an external filter.


The forum trailvoy.com will help you out tremendously. You could chase that gremlin for a very long time. I know, I own an envoy, and chased many gremlins in that vehicle.
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#4514093 - 09/12/17 09:44 AM Re: GMC Envoy Rough Idle [Re: carguy996]
BrianF Offline


Registered: 02/25/15
Posts: 551
Loc: Sask, Canada
Sounds like you have a good plan. I still love my 2006 Tb. Runs strong but always has a hiccup or two in the platform.

When cleaning the MAF and the throttlebody, disconnect the battery for about 30 minutes to let the computer relearn on clean components. As well, remove the throttlebody from the intake to clean it fully.

The other, non related thing is the transfercase. These Autotrak 2 equipped vehicles need the fluid changed every 50,000 miles apparently.
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#4514112 - 09/12/17 10:00 AM Re: GMC Envoy Rough Idle [Re: carguy996]
JTK Online   content


Registered: 08/14/03
Posts: 10589
Loc: Buffalo, NY
I owned a 2005 Trailblazer LS 4x4 for a few years. Like said, if there's no check engine light, it could be a dirty MAF sensor. Some of the earlier inline 6 powered Trailblazers didn't have a MAF (used computer modeling instead), but they started putting them back in, in 2005. Could be a lazy O2 sensor too, but it's all kind of a guessing game at this point. Could be old fuel even.
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#4514128 - 09/12/17 10:18 AM Re: GMC Envoy Rough Idle [Re: carguy996]
mk378 Offline


Registered: 09/27/15
Posts: 1421
Loc: USA
Check for air leaks. Any unmetered air entering the engine through a leak after the MAF sensor will lean out the idle.

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#4514252 - 09/12/17 01:18 PM Re: GMC Envoy Rough Idle [Re: carguy996]
ChevyMan93 Offline


Registered: 06/05/17
Posts: 131
Loc: Tennessee
Good suggestions here. I would personally clean the throttle body, clean the maf, change plugs, change air filter and check/replace fluids.

More than likely a dirty maf and throttle body. Make sure to use an actual maf cleaner and an actual throttle body cleaner. Don't use some generic brake parts cleaner or something. Use the right stuff, I've never had issues using crc maf cleaner or throttle body cleaner.

Good luck!
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#4514337 - 09/12/17 03:36 PM Re: GMC Envoy Rough Idle [Re: carguy996]
JBinTX30 Offline


Registered: 09/08/14
Posts: 476
Loc: Texas
More than likely a dirty throttle plate. I would take it off the car completely and clean it.
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#4516602 - 09/14/17 10:04 PM Re: GMC Envoy Rough Idle [Re: carguy996]
another Todd Offline


Registered: 05/15/06
Posts: 2205
Loc: Lakeside CA
They did have valve seat problems which caused a rough cold idle. Got better when hot.
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#4519194 - 09/18/17 07:51 AM Re: GMC Envoy Rough Idle [Re: carguy996]
carguy996 Offline


Registered: 10/26/06
Posts: 260
Loc: Illinois
Wanted to provide an update....after replacing the plugs, doing a throttle body cleaning, air filter, MAF cleaning and SeaFoam upper intake clean, I still had a slight miss. Found the #2 coil on plug to be faulty, replaced that and it now runs perfectly and very smooth. Also did an oil change. Fuel Filter will be next.
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#4519251 - 09/18/17 08:54 AM Re: GMC Envoy Rough Idle [Re: carguy996]
Bgallagher Offline


Registered: 04/17/12
Posts: 3159
Loc: Boston, MA
Originally Posted By: carguy996
Wanted to provide an update....after replacing the plugs, doing a throttle body cleaning, air filter, MAF cleaning and SeaFoam upper intake clean, I still had a slight miss. Found the #2 coil on plug to be faulty, replaced that and it now runs perfectly and very smooth. Also did an oil change. Fuel Filter will be next.


Great work! I imagine all the cleaning and fixing the coil probably made a big difference.
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2017 Chevy Traverse - 28k - Delco Dexos 1 and PF63
2014 Chevy Equinox - 22k - Delco Dexos 1 and PF457G
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