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2005 gmc envoy_slt
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Discussion Starter · #1 · (Edited)
Hello everyone -- this is my first post -- so please be patient with me :)

We have an 05 Envoy which we have owned for about 5k mi -- has 65k on it now - we are the second owners.

service engine soon light is on as of today but have not checked the code -- my husband is the one who actually drives it (and is definitely not the tech-y one of us) so all of this is hearsay

He had complained a couple weeks ago about the tach jumping a couple hundred RPM while driving a constant speed on a flat road (about 60 mph) -- I drove it a few days -- nothing out of the ordinary

Today, while he was driving in town he said the problem was much worse. instead of jumping a couple hundred rpm up/down it was closer to 500, and you could hear/feel the problem.

Anyone heard of this or had any experience with something similar?? Did some research on here and am thinking its possibly a torque converter??

I just dont want to let the converter mess up my transmission in the future (works well as of now) - I know extended warranty is not going to cover it if the SES code is not for it

Could a transmission flush possibly help the problem? ATF levels are normal

Unrelated -- a week or so ago SES light came on w/ code P0410 (secondary air injection system) -- did some research pretty sure its the check valve as I can hear the pump working on a cold start -- had the light reset. not worried about emissions standards so much (we live in Iowa), BUT it is possible that the return of the engine light is from that code!

ANY RESPONSE APPRECIATED!!
 

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2002 gmc envoy_slt_xuv
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Getting the code read is a priority and post the exact results.

The rpm fluctuation is probably caused by a dirty throttle body. Whether or not the dirty throttle body is the root cause of your problem it's still a good thing to clean it up. It's cheap and easy to do. There are a number of threads with step by step instructions which you can find by using the search function.

You mentioned that you can now hear and feel the problem. Describe what's happening.
 

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2003 gmc envoy_slt
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I had a similar problem @ about 35k miles.

It only happened when I was in A4WD, but not always. It almost felt like someone was pumping the brakes just slightly. A kind of jerky feeling.

I drained and replaced the transfer case fluid and all is good.

Do you know the maintenance history of the truck? The t-case fluid should have been changed at 50k miles.

Oh, and :tiphat Welcome :tiphat
 

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2005 gmc envoy_slt
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Discussion Starter · #4 ·
by hear/feel -- i just mean you can hear it rev a little then back off and feel it pull forward some when it revs up. Its not like it is downshifting when it backs off.

I am driving it (instead of my husband) so hopefully I can paint a more accurate picture soon.

The problem has only occured in 2HI, as far as I know. & I have no service records -- we bought it from a GM dealership (basically because we needed to get rid of my husbands old passat that needed $2500 put into it)

Envoy needs an oil change anyway so I am going to have my mechanic (not a slimeball -- i dont even call the dealership anymore because they always want someting) check it out -- im hoping that it is just some fluid needing changed!

Thanks for the info! I'll keep you posted! :)
 

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2009 chevy
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I think you are on the right track looking at the torque converter.

Think of 2 fans facing each other, turn one on and the 2nd one will spin from the wind hitting the fan blades.

The torque converter works the same way, with the transmission fluid replacing the air.

Both of these examples have the tenancy to "slip". Apply a little resistance to the 2nd set of blades and they will spin slower than the 1st set of blades.

With a vehicle, this is a huge generator of heat and a waste of gas.

In a vehicle, this slippage is noticed, by the driver, as an increase in engine rpm.

At highway speeds, modern torque converters "lock up".

An electrical solenoid connects the drive blades to the driven blades and slippage is eliminated.

It is possible, your converter is not "locking up"
 

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Discussion Starter · #9 · (Edited)
Thanks for the thread -- I actually read through it a few days ago, showed my husband the video, & asked him if that is how it acts for him. He said yes -- but it changes up/down more quickly.

It is really strange that it won't do it for me -- how often does yours behave that way??

Did you ever figure out what was going on? Your problem seems to be the most similar to ours out of everything I have searched through on here.

65k seems a little young for a new tranny! I find it a litte funny that I am borrowing my dad's old Tahoe w/248k on it, so that my 65k truck can get fixed!
 

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2003 gmc envoy_slt
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Thanks for the thread -- I actually read through it a few days ago, showed my husband the video, & asked him if that is how it acts for him. He said yes -- but it changes up/down more quickly.

It is really strange that it won't do it for me -- how often does yours behave that way??

Did you ever figure out what was going on? Your problem seems to be the most similar to ours out of everything I have searched through on here.

65k seems a little young for a new tranny! I find it a litte funny that I am borrowing my dad's old Tahoe w/248k on it, so that my 65k truck can get fixed!

Well EVERY trans shop I went to said it was the solenoid that locks in the T.C. But i Checked on the forum and Sparky was telling me its just the valve and the kits on ebay only cost about $40. I ended up buying the better kit that fixes a few other problems with our transmissions from the same guy and it fixed EVERYTHING. I cost about 120 shipped to my door. Went out of town to a shop that installed it in 4 and half hours (that was a long wait in the waiting room) and $380 later my transmission shifts better then new. I def. dont think your transmission is going out. The test I was told to do is to go at highway speeds, hold the RPM and speed at a constant rate with one foot, and then just barely tap the brake, just enough to turn the lights on. Thats what I was doing when i took that video. It would more abruptly change like you describe after about 2 hours of driving (trans fluid is warmed up)
 

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2003 gmc envoy_slt
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2005 isuzu ascender
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Trans problem?

It's not clear to me from the post exactly what this problem is. This could be a tach stepper motor on the way out. If it really is, that's a lot cheaper than a trans. 500 RPM at highway speeds (60) would be 20-30 MPH change.
 

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2003 gmc envoy_slt
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It's not clear to me from the post exactly what this problem is. This could be a tach stepper motor on the way out. If it really is, that's a lot cheaper than a trans. 500 RPM at highway speeds (60) would be 20-30 MPH change.
Where you are right only if the transmission/ TC are locked in, otherwise its just slipping.. If it slips i could at 5k RPM and still go the same speed...
 

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Discussion Starter · #17 ·
according to my husband, it changes @ in town & highway speeds.

STILL hasn't done it for me. when I tap the breaks while driving ~60 ish it RPMs go up ~100. sits right around 2100 @ 74mph on my hour long commute.
 

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according to my husband, it changes @ in town & highway speeds.

STILL hasn't done it for me. when I tap the breaks while driving ~60 ish it RPMs go up ~100. sits right around 2100 @ 74mph on my hour long commute.
I am not sure, but my guess is that valve is going out. I would almost say give it more time untill you get a code, i got a (P1780) i believe. The kit i bought is specifically to fix it.
 
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