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2005 chevy trailblazer_ls_ext
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6 Posts
Discussion Starter · #1 ·
As the subject says, yet another rough idle question...

Vehicle: 05' TB I6 w/102K miles

Problem: Intermittent rough idle. RPMs drop from 600 down to 400, then back up. Seems like TB is going to stall, but has to actually do so. Doesn't seem to matter if AC is on or off. CEL is NOT on (and hasn't been).

What I've done (not necessarily in order):

1. After reading many posts about this, I did clean the throttle body (was dirty, but nothing compared to some pics other users posted). I did disconnect the battery while doing this.
2. Seafoamed via gas tank and vacuum line (it did smoke, although not as wild as some of the videos I saw)
3. Checked all the vacuum lines I could find for cracks, rot, etc. Looked OK.
4. Cleaned business end of MAP sensor (was a little "oily", but not caked or anything)
5. Pulled a couple of plugs for a look. They didn't appear to be burnt or anything. I did have a slight amount of oil in a couple of the wells (nothing above the plug threads though).

Other:

1. Plugs have about 30K on them.
2. This MIGHT be happening more as the temp increases (coastal South Carolina - getting warm down here). Unsure if this is really true, or if I'm just more and more sensitive to it.


So, anyone have any thoughts? Thanks for any assistance...
 

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2002 gmc envoy_sle
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1,380 Posts
The only thing I can think of right off hand is are the plugs AC-Delco? If not, that can lead to a rough idle.
 

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2004 gmc
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26,181 Posts
Some folks like me have reported success changing the CPAS. Especially if you also get intermittent SES lights. Ever get a code thrown?

100K is about time for the upstream O2 sensor. Check the sensor data if you have a good scan tool to see if it's slow or fast-changing. Use Delco.
 

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2005 chevy trailblazer_ls_ext
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6 Posts
Discussion Starter · #4 ·
Some folks like me have reported success changing the CPAS. Especially if you also get intermittent SES lights. Ever get a code thrown?
Nope, it hasn't thrown a code for the duration of this problem. I wish it would! :)
 

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2004 chevy trailblazer_lt
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1,298 Posts
As was already asked, are the plugs AC Delco 41-103? Some members have had
problems with other types after they've put a few thousand miles on them.

Also, check to see if your CPAS is leaking oil at the electrical connector. Mine is.
very slightly, (and I'm eventually going to get around to swapping it). The truck
started having the same idle fluctuations other members have described around the
time I noticed the seepage. I had already cleaned the throttle body, and the truck
had been running nicely. It seems to do it more when it's warmed up. No codes, just
an intermittent drop/rise in idle that I can't associate with any other engine accessory
turning on or off (spent quite a bit of time watching sensor data to see if I could nail
something down).

Good Luck!

Chris
 

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2005 chevy trailblazer_ls_ext
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Discussion Starter · #6 ·
As was already asked, are the plugs AC Delco 41-103? Some members have had
problems with other types after they've put a few thousand miles on them.
No, the current plugs are not AC Delco [hides face in shame], they are Autolite I believe.

Thanks for the replies folks, I appreciate the help.

Brian
 

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2004 chevy trailblazer_lt
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1,298 Posts
Heh...well, swapping the plugs'll be cheaper than buying the CPAS usually. You
might just want to start with that and see what happens. Just be careful with the
coil packs, and make sure they're seated properly when you put them back on. A
little dielectric grease on the boots, or at least checking them over for carbon tracking
or cracks wouldn't hurt either.

Cheers-

Chris
 

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2005 chevy trailblazer_ls_ext
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6 Posts
Discussion Starter · #8 ·
Update

Well, went after work and picked up new AC Delco plugs as recommended and put them in this evening.

So far it seems to be running smoothly with no miss.

The real test will be when the Mrs. drives it around tomorrow.

Upon taking the old (30K) plugs out, #4 was cracked in many places (2 cracks the length of the ceramic, several others coming off those). Is that an indication of a poor quality plug, or should I be alert to something which can cause that? As I think I noted earlier, there was a small amount of oil in the well with the plugs, but generally very little (not anywhere close to the ceramic).

Thanks to everyone for their reply in this thread (and all similiar ones which helped too!)

Hopefully I still think this is fixed tomorrow night!

Brian
 
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