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2005 chevy trailblazer_lt
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4 Posts
Discussion Starter #1
Hey guys,

I have been scouring this site for a couple weeks now trying to find a solution. First off, I have 99k miles on my 05 TB. Let me give you a walk through with my issue:

Vehicle was running great, but I was approaching 100k miles so I decided to swap the spark plugs with the AC-Delco Iridium plugs. That went smooth. I also removed the throttle body and cleaned it, then reinstalled it. I was very gentle with the throttle body (which was filthy). The key was never in the ignition and the battery was unhooked for over an hour for this entire tune up.

I get everything back together no problem, but now I get a shake/shimmy from the truck when in gear and at a stop after sitting there for 10 seconds or so. The RPMs idle around 600, but jump +/-100 when the rough idle occurs. Running the AC doesn't seem to have any effect, better or worse. When in park/neutral there is still fluctuation in the rpms, but I don't feel it as much and it is more consistant. I have put over 300 miles on the truck since I tuned it up and it runs amazing as long as I am not at a stop. I pulled it all apart again and looked it over and it seems like there are no obvious problems with unhooked lines/wires. There are no codes or lights flashing.

Thanks to this awesome site, I have been able to gather a lot of information.
So here we go with possible solutions:

-Unplug the battery to allow the pcm to relearn with a clean throttle body.... I did that twice now. Didn't seem to help.
-Check for vacuum leak/damaged gaskets. I looked over everything and couldn't find a leak, so I pulled the resonator and TB back off and looked for a cracked line/pinched gasket. Nothing, all looks good. Gasket wasn't hard or cracked.
-I see motor mounts as a solution a lot on here, but that cannot possibly be my issue as it was fine before the tune up and there is an actual change in idle rpms, so it isn't just a vibration issue.
-I am in the process of getting my PCM tuned from PCMofNC, so last night I put in my loaner (stock) PCM and that didn't solve the rough idle. I did the tune over a week ago.
-This doesn't seem to be an issue with exhaust vibration, once again because of actual idle rpm fluctuation.
-Perhaps a misfire/unseated coil pack boot? If that was the case, wouldn't the motor run bad (like really bad) all the time? The truck runs/accelerates perfectly on the highway.
- I only unplugged a couple sensors during the tune up, so I unplugged them again to see if I damaged or bent one of the contacts. Nope, they look good.
-I have ran 2 tanks of gas though from 2 different stations...so I don't think it is a bad gas issue.

Even though I am not throwing any codes.....from what I can tell, I am left with possibly a damaged throttle body from cleaning it? Or a lazy/going bad O2 sensor. Or possibly an IAT issue. This vehicle doesn't have a MAF sensor, so that isn't it. I guess I cannot wrap my head around how doing 2 basic things (spark plugs and cleaned TB) can create such a headache.

Guys, I am losing it.:hopeless I love my truck, but this sucks. If there is any insight floating around out there I would appreciate it.

Thanks,
Jeremy
 

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2005 chevy trailblazer_lt
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4 Posts
Discussion Starter #2
Slight update:
I took it all apart again and replaced the o-ring between the throttle body and intake. I also seafoam'd the truck (half in the vacuum line and half in the gas tank). The intake manifold bolts are notorious for loosening over time, so I checked them and they were fine. Maybe slightly loose, but I didn't want to over tighten them. I had heard of the bolt backing out an 1/8", which wasn't the case for me.

These did not help the erratic idle rpm's. It feels like a slight vacuum leak, but I cannot find it by sight or sound. Ideas for easy/at home vacuum leak detection?
 

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2005 chevy trailblazer_lt
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4 Posts
Discussion Starter #3
Another update:
I pulled my CPAS (VVT solenoid) hoping to find tons of metal shavings and a damaged solenoid, but that was not the case. It seemed fine, but I cleaned it and made sure the solenoid still moved freely and re-installed it. No change to the rough idle.

On a lighter note, I installed my tuned PCM from PCMofNC last night. I love it! I went with this set up: tuned for 91 gas, no towing, shift rating of 2. I have noticed much better throttle response, crisper shifts, and better shift points. The truck no longer revs up really high in order to downshift. I am skeptical this may reduce my transmission life due to the harder shifts, but I will cross that bridge if it comes along. Meanwhile, the truck is much more fun to drive! :woot:

Now, if only I could figure out this darn idle issue....:duh:
 

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non_gmt360 trailblazer_lt_ext
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241 Posts
Damn man.. Almost a week and half and over 220 views and no help at all.. You have went over all the stuff I would have done.. But I'm no expert Like the guys who used to be here..

You should really follow this link: http://bit.ly/1E2eIwa click on the first link and join over there. All the guys that have shared all of the useful knowledge here have moved over there. There is someone There that can help you for sure.
 
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