03 Trailblazer Rough Idle no codes - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 09-19-2012, 11:36 PM
bimmerrx7 bimmerrx7 is offline
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2003 Chevy TrailBlazer LT
Summit White 4.2L I6 2WD
Join Date: Aug 2008
Location: Birmingham, Alabama
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03 Trailblazer Rough Idle no codes

03 Trailblazer. Started noticing a slight vibration at idle around 150k miles. Replaced the plugs with OEM AC Delcos, new fuel fitler, and cleaned the throttle body. The vibration became worse over time. Replaced the fuel pressure regulater due to leakage on the old one, cleaned the throttle bottle a second time, still no luck. Changed the camshaft solenoid this week after diagnosing it was bad, the rough idle is still there. It's bad at times so much so that my bug guard vibrates against the hood. It's worse in drive and reverse. I've checked the motor mounts and they're good. I've not only unhooked the battery each time I changed a part, but also cleared the codes via my Auto Tap OBDII program and tester. I cleared codes just as a procaution though none ever showed up. I checked for a vacuum leak by misting water over the engine at idle, didn't detect any fluctuation in the engine idle. My rpm guage hovers around 600 at idle, and even though I can feel the rough idle, the needle really doesn't fluctuate. The engine has never stalled. I'm at a loss on what to try next. I've heard coils can become lazy without setting a code, but I've never logged a misfire. The engine does seem to crank and shut off a little less smoothly than it used to. Gas mileage hasn't changed and the power seems to be the same.

Anyone have a clue what's causing my issue?
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  #2  
Old 09-20-2012, 07:32 AM
NJTB04 NJTB04 is offline
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2004 Chevy TrailBlazer LS
Pewter Metallic 4.2L I6 4X4
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Check for intake manifold leaks, make sure the exhaust manifold bolts are tight. When you have the scanner hooked up, check the engine temp is around 200 when warmed up.
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  #3  
Old 09-24-2012, 05:19 PM
chevytruckluvr chevytruckluvr is offline
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2006 EXT & 2002 regular Chevy 2006 TB EXT / 2002 TB
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02 TB rough idle no codes

bimmerrx7, I have the same issue with my 2002 TB. Started noticing the rough idle a week or two ago. Changed the spark plugs but still the same. I have 250,000 miles. Can anyone give us some ideas??
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  #4  
Old 09-24-2012, 06:37 PM
NJTB04 NJTB04 is offline
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2004 Chevy TrailBlazer LS
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Bimmer;
I re-read your post and you said you checked for vacuum leaks.
My best suggestion from here is to Sea Foam it, as it may be a carbon buildup inside the engine. There's a procedure in a post on this forum. It will smoke like crazy. Fill it up with gas and throw another bottle of Sea Foam in the gas tank.

If that don't at least improve the idle, do a compression test. Were any of the plugs oily when you pulled them out?
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  #5  
Old 09-24-2012, 09:51 PM
bimmerrx7 bimmerrx7 is offline
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2003 Chevy TrailBlazer LT
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Quote:
Originally Posted by NJTB04 View Post
Bimmer;
I re-read your post and you said you checked for vacuum leaks.
My best suggestion from here is to Sea Foam it, as it may be a carbon buildup inside the engine. There's a procedure in a post on this forum. It will smoke like crazy. Fill it up with gas and throw another bottle of Sea Foam in the gas tank.

If that don't at least improve the idle, do a compression test. Were any of the plugs oily when you pulled them out?
There was some oil in several of the plug wells. I replace each coil last weekend with a new one, one at a time and did not notice any new oil. If the gasket is leaking, it's very little over time. I change the plugs for the first time around 150k. After changing the crankshaft position sensor on Saturday, the idle is actually a little worse, but it's a very steady roughness if that makes sense. Never once does it appear that the engine might stall.

I'm taking it to the dealer for a $95 diagnostic scan and re-flash of the PCM, do you think their scan would show compression issues?

Thanks.
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  #6  
Old 09-25-2012, 07:25 AM
NJTB04 NJTB04 is offline
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2004 Chevy TrailBlazer LS
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It might, depends on if the rough idle is caused by a misfire and how bad the misfire is. After all the diagnosis and work you did, I'm still leaning towards a carbon problem.
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  #7  
Old 09-27-2012, 07:10 PM
bugeyed bugeyed is offline
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2004 Chevy TrailBlazer LS
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You said that you checked the motor mounts & they were good. You do know that a visual check will not tell you if they are bad. How do you know they are good? If the vibration is around 10Hz at idle when in gear, it is likely to be the motor mounts. I have the same symptoms & am planning to change mine. There are several threads here that support my diagnosis. If you fix it without changing mounts, please report here.

k
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  #8  
Old 07-02-2013, 12:23 AM
sandman03 sandman03 is offline
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2003 Chevy TrailBlazer LS
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rough idle 03 trail blazer

I found that the motor mounts go bad on the 03 trail blazers and make you think you have a rough idel when you dont is just a vibration . Do not replace them with after market mounts i learned the hard way ,they only lasted a couple of years and and went bad . If they look sunken in they are bad . I think they are liquid filled . Dont get the dealership to do it they will charge you big time . I bought the parts and had a transmission shop replace the front 2 mounts for $150 . Smooth running now . Very easy to want to start trying to replace plugs , sensors when the problem is a vibration issue . the 4.2 straight 6 has to have mounts that are in good shape to stop the vibrations .
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