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2002 gmc envoy_slt
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85 Posts
Discussion Starter #1
I so hope somebody has a clue as to what is causing my '02 Envoy's (182k) engine to occassionaly stumble/hesitate(?) while driving.

I'll be driving and when I get up to around 35 - 45 MPH sometimes my truck will stumble and I'll notice the RPMs go down then back up. I feel it lightly jerking, but when I step on the gas it accelerates and all is good.

It won't do it if I accelerate at a quick pace. Not flooring it though. It seems to do it more when I am going uphill and now sometimes when I am going up a road with a slight incline, but only after around 30 MPH. It will do this even up to around 70 MPH.

At first it only happened when I would go up a steep incline going up to the freewat, but now it doesn't take much of an incline, if one at all.

It doesn't do this all the time, but it is happening more often.

I just got my emissions inspection sticker, so my O2 sensors and catalytic converter are good.

My spark plugs have 92k miles on them.

It turns on perfectly, idles smoothly, and accelerates well when stepped helfway down. If I floor it she'll accelerate as good as she always has.

Help please. I've tried searching on this site but couldn't find anything similar.

Thanks in advance, any help would be appreciated.
 

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2002 chevy trailblazer_ltz
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3,250 Posts
And the last time the throttle body was removed and cleaned was when?
 

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2002 chevy trailblazer_ltz
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3,250 Posts
Cleaned Throttle body and still the same.:(
You removed it from the engine and cleaned BOTH sides, and battery was disconnected for at least 35-40 minutes while doing it?
 

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2002 gmc envoy_slt
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85 Posts
Discussion Starter #6
Tranny fluid full, and yes throttle body cleaned in the correct method.

Also just replaced air filter.

All is still the same.

What is new is that it will do the surging/stumbling motion either consistently when on the freeway (20 minutes) or not at all. If it does it, even stepping on the gas a bit harder won't make it go away like before.

But it is still just fine at idle and during non-highway driving, going no more than 40 MPH of course.

I'll be taking it to the dealership tomorrow to see what's wrong.

I'm thinking it's likely the throttle position sensor or fuel pump. Hopefully I'll be lucky and it'll be something less expensive like the coils.

Oh well, I'll keep you guys informed for future reference.
 

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2002 gmc envoy_slt
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85 Posts
Discussion Starter #7
Solved!!!!

I took it to the dealer and they found a TCC (torque converter cluth) code.

So it was handed over to their transmission guy who noticed it was low on fluid about 2 quarts. He filled it up and took it for another drive and no problems whatsoever. Of course he found there's a minor leak in the transmission cooler lines that caused this, but he said so long as I keep it full I should be fine until I change them.

Although I feel silly that something so minor caused such a headache, I'm glad I didn't go putting on things that are the usual suspects (fuel pump, throttle position sensor, coils, etc.). So for less than $60 I got it my vehicle correctly diagnosed and now I'm worry free.:)
 

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Basic Vendor- Skid Plates
2007 chevy trailblazer_ls
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3,700 Posts
I took it to the dealer and they found a TCC (torque converter cluth) code.

So it was handed over to their transmission guy who noticed it was low on fluid about 2 quarts. He filled it up and took it for another drive and no problems whatsoever. Of course he found there's a minor leak in the transmission cooler lines that caused this, but he said so long as I keep it full I should be fine until I change them.

Although I feel silly that something so minor caused such a headache, I'm glad I didn't go putting on things that are the usual suspects (fuel pump, throttle position sensor, coils, etc.). So for less than $60 I got it my vehicle correctly diagnosed and now I'm worry free.:)
We've been talking about this on offroadtb, and James did the repair for it. I seriously doubt that the extra fluid will fix it in the long term, as this is a pretty common problem for GM trucks, regardless of what the dealer wants to tell you.

I can't link to ORTB or the 'nation (without getting banned) since everybody jumped ship, but JamesDowning did a write-up with pictures on how to install the shift kit that gets rid of the PWM function of the TCC, entirely. It's one of the recent topics on offroadtb. My dad didn't want to mess with it on his '00 Silverado, and just paid a local transmission shop $250 or something to do it.

Mike
 

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2002 chevy trailblazer_ls
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23 Posts
Thats what i had tranny cooler line leak! 600 bucks to fix in MA. Just replace them all. It is common for them to rust but mine lasted 10yrs so i cant complain. I read several write ups on replacement off trailvoy and it seems that if u have small hands they may be accessible otherwise u will have to drop the tranny. I didnt want to mess with dropping it so i brought it in. Good luck!
 

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2002 gmc envoy_slt
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Discussion Starter #10
Well a few weeks back I replaced all tranny cooler lines and she's been shifting as good as new.

The mechanic told me too that it was normal at this amount of years (10) and that I'm good to go for another 10 years. Which is a good thing because that's about how much longer I plan on keeping it. :D
 

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2004 gmc envoy_slt_xuv
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7 Posts
If I understand this correctly, the motor was dropping rpms and surging hesitating at times and this was fixed by adding tranny fluid to the tranny ?
;)
 

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2002 chevy trailblazer_ltz
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If I understand this correctly, the motor was dropping rpms and surging hesitating at times and this was fixed by adding tranny fluid to the tranny ?
;)
If the fluid level was low, it can cause the torque converter lock-up clutch to engage and dis-engage, making it feel like the engine is surging.
 

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2004 gmc envoy_slt_xuv
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I have an 04 envoy xuv with the 4.2 and it seems to be doing the same. As I drive down the road the motor surges and almost stalls i push on the gas pedal and the rpms increase but the engine is bogging down and then the rpms jump to like 4500 almost like i was tied to an anchor and the chain broke. I just completed a trip from NC to PA back to NC and it progressively has gotten worse. taking the advice of area mechanics i have replaced the Cat. the fuel pump, cleaned the throttle body (again). and i am now heading to the auto parts store for some dextron III as I am 1/2 a quart low. If this does not fix my problem any suggestions as to what it may be . :crazy:
 

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2002 gmc envoy_slt
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Well a few weeks back I replaced all tranny cooler lines and she's been shifting as good as new.

The mechanic told me too that it was normal at this amount of years (10) and that I'm good to go for another 10 years. Which is a good thing because that's about how much longer I plan on keeping it. :D
Did you replace them yourself, is there a write up how to do?
 

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2002 chevy trailblazer_ls
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Check for leaks from the cooler lines . They commonly rust . They r to long lines side by side 1 for return from transmission on passangers side only about a half inch in diametier. May be behind a heat shield
 

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2004 gmc envoy_slt_xuv
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Added fluid to tranny , still same issues ! This morning It was the worst it has ever been Motor would race and then almost stall race again then almost stall. I took it to the dealership and the tech took it for a drive. says it seems to be vapor locking, put it on the rack to measure fuel pressure and it measured good but then hit the button on the tester to fill the bottle and it dies instantly. wanted to check something else so he starts it and then pulls the relay for the pump again it dies instantly. he says it should have kept running for a few seconds before quitting but he's still not certain what it could be. Asked if I could leave it for a few days to figure out what is wrong with it. HONESTLY ? WHAT OTHER CHOICE DO I HAVE !!!!:confused:
 

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2004 gmc envoy_slt_xuv
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well it has been at the dealership for 4 days now and all i have to show for it is a bill for $636.86 and an Envoy that still has the same issues. They put a new pump in no change, they updated the computer no change, they checked the temp on the transmission temp sensor in 3 different times "operates as designed" , still no change. The one that got me was when one of the mechanics said he even tried cleaning the MAF sensor, One mechanic rolled his eyes as I explained to the other it doesn't have one ! Great the dealership has hired lying morons !so what did they actually do to my truck !Oh disputed the bill after that comment and all they charged me for was computer hook up @ $86 . Could this possibly be a throttle positioning sensor malfunction even if it doesn't throw a code ? :hissy:
 

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2004 chevy trailblazer_lt
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Bumping this thread. I have a 2004 with 57k very well maintained and same issue. Not throwing any codes.

Last year had similar problems and threw an O2 sensor code and had dealer put a new one in and it fixed the problem, worked fine for about 10k miles. Now this:worried:

AZ truck, no rust, no leaks, no off-road use, :confused:
 

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2004 chevy trailblazer_lt
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Changed the fuel filter last night and still have idle issue but did not have time to run on the freeway. Noticed the AC compressor kicking on and off while idling was almost killing engine. I'm thinking its time for another throttle body cleaning. Will update with results.
 
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