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2004 gmc envoy_slt
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I have a 2004 gmc envoy 4x4 4.2l 6 cyl. I changed the battery and the idle is very eratic. the engine died on me 4 times while going to work. I have found that if i turn the ac off on my climate control the engine runs great. If turn on the defrost (ac comes on) the idle is very slugish until it kills the engine. HELP PLEASE
:bonk:
 

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2002 chevy trailblazer_ltz
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Disconnecting your battery has allowed the PCM to reset to original factory default settings. Unfortunately, your throttle body is dirty, but you didn't know it until now because the PCM has been altering the way the engine runs to compensate for it.

Now that the computer thinks everything is great, it's not taking into account how dirty the Throttle Body is, and that's where your getting the bad idle.

Remove and clean the throttle body as soon as you can, (and yes, disconnect the battery while you do it again), and after it's all clean and you reconnect the battery, all should be well.:yes:

here's the "how to":
http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91
 

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2004 gmc envoy_slt
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Discussion Starter #3
thanks, petevw

I will get cleaner and try this in the morning. Let you know how it turns out....:hail::thx
 

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The throttle body was really dirty. Bought a can of throttle body cleaner from local parts house and followed your link.

Started engine and turned everything on climate control on and the engine ran perfect.

Thanks again. :thx :thumbsup: :D
 

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2003 chevy trailblazer_ls
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glad it worked out for you....
You probably saved yourself about $150 by doing it yourself.
 

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So I had Pep boys change the Thermostat today, he unhooked the battery in doing it and now it stalls in idle whenever the AC or heater is turned. He claims that the computer needs to relearn since it has been reset, but driven 20 miles and still no change. Any suggestions?
 

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2004 chevy trailblazer_ls
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:iagree:

Iv'e had shops and part stores tell me I needed a new ac compressor after I changed the battery...

Good thing I found this forum in time, WELCOME!!

Take you throttle body OFF YOUR TRUCK and THEN clean it. follow the link on post 2 step by step
 

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2003 chevy trailblazer_ls
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like they said. clean the throttle body as per post # 2.
 

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I've read the threads on battery changing and the fact that the PCM has to relearn everything so the idle can be lumpy etc if the throttle body is dirty. So when i had to replace my battery just before Christmas (-16C in the garage, day before a 300km trip with wife and 2 kids - they never fail in the middle of summer when you arent going anywhere do they?) I was fully prepared to have the thing drive like a dog. Its got 110,000 KM on it, 72K of which I didnt do so I had no idea how bad it might be.

So when I put the new battery on (about 3 hrs after taking the old one out), I was surprised that it started OK, and nothing seemed different. Even the radio presets were the same. Idle was a solid 600rpm (after warming up) and I've not experienced any issues with dying at all.

Don't get me wrong, I'm not complaining - the last thing I wanted to do that night was to try and clean a throttle body. But I would be interested as to why this occurred. Did I miss a scenario where the PCM retains its memory (e.g. because of some sort of capacitor/backup battery) unless its disconnected from power for a long time? Any ideas? (Or am I being stupid?)
 

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2003 chevy trailblazer_ls
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it will idle fine...
the problem comes when you turn on the AC...
at that point you will learn if the throttle body is dirty...
turn off AC.. and it idles fine again.
Have you used the AC?
 

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2005 chevy trailblazer_ls_ext
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it will idle fine...
the problem comes when you turn on the AC...
at that point you will learn if the throttle body is dirty...
turn off AC.. and it idles fine again.
Have you used the AC?

So when i had to replace my battery just before Christmas (-16C in the garage, day before a 300km trip with wife and 2 kids . . .
Seeing as how he said it was -16C in the garage, (about 3F) I rather doubt it. Even if he turned the defroster on, the compressor clutch wouldn't engage because of the low temp!

One of two things is happening here. Either the TB isn't dirty, or because the a/c clutch isn't engaging he will not get the poor idle!
 

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yeah, I noticed that after I reread. then wondered.. maybe he tried using the defrost- which would have turned on compressor... but yeah, like you said.. even then it wont come on because of the cold temps. Good catch.
 

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Thanks guys - I knew I'd missed something. I'll be honest I leave the Climate Control on all year - but as you say, its probably too cold for the compressor to kick in to cool the air.

I'll wait and see what happens when it warms up a bit and the A/C starts working. At least it will be warmer when I (probably) have to clean the throttle body :)
 

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So while changing the thermostat Pep boys disconnected the battery and it idled. They refused to clean the throttle boy and did a scan tool on the car and it stated that the air filter was dirty and after we changed that the car improved, still want great but better. IS there any other factors that can be affecting performance? What do you guys recommend about the spark plugs?
 

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just clean the throttle body yourself... youll avoid all the back and forth with Pep Boys...
Clean the throttle body an then see if it still acts up. If it does, then something else is wrong..
but the symptom you described are fixed by cleaning the TB.
 

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2003 chevy trailblazer_lt
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Can I assume I will have to clean the TB as well when I start using the vehicle again in the spring - I have stored the Trailblazer for the winter and removed the battery (cold storage).
If it gets a bit warmer maybe I will clean the TB before I re-start the Trailblazer to avoid any possible problems.

Being in Canada (no Pep Boys etc.) any Canadian members have suggestions for which cleaner would be the most effective?

Thanks,
David.
 

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if youve never cleaned it- its possible it can give you trouble..
But remember-- the car runs great.. until you turn on the AC.
thats when the erratic idle pops its head.... turn off AC and it idles smoothly.
 

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if youve never cleaned it- its possible it can give you trouble..
But remember-- the car runs great.. until you turn on the AC.
thats when the erratic idle pops its head.... turn off AC and it idles smoothly.
It was actually a reasonable day in Toronto today so uncovered the Trailblazer, put in the battery and went for a ride - seems to run perfect but like you said the AC didn't come on as it was only about 25 F degrees out.

I try to run the vehicle about once a month (weather permitting) just to keep everything moving and avoid flat spots on the tires.

Since the Trailblazer has about 90,000 miles, I think I will clean the TB and change the spark plugs when it warms up a bit more.

Regards, David,
 

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I had the exact same problem as the original poster, replaced the battery, and it idled rough, then quit when the AC kicked in. I did what the #2 poster suggested and Volia! It works like a charm!

Dang glad I found this website, that's fer sure.
 
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