Rough Idle - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 04-23-2012, 10:27 AM
uga06dawg uga06dawg is offline
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Rough Idle

My 02 Trailblazer LTZ with the V6 has recently started idling rough. It only happens for a short while after start up. I notice it when I stop at red lights. It just runs really rough causing vibration but it smooths out if I put it in neutral. However after driving at 70 mph for about 30 mins on my way home from work it no longer idles rough. Any thoughts?
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  #2  
Old 04-23-2012, 12:09 PM
Loverotties Loverotties is offline
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Really hard to say because someone switched motors in it (v6 instead of the I6)that came with it.
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Old 04-23-2012, 01:18 PM
uga06dawg uga06dawg is offline
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I'm sorry it is the L6 engine (typo). It is the original engine.
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Old 04-30-2012, 02:38 AM
Sirjonathon Sirjonathon is offline
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#PIP4013C: In-line Truck Engine Misfire at Idle - (Aug 24, 2011)

I found the following tech bulletin concerning rough idle or misfires on our TB's. The fix is expensive. My understanding is that the misfire is only at idle so it won't hurt the engine if you decide not to replace the head. It's definitely an annoyance tho.


#PIP4013C: In-line Truck Engine Misfire at Idle - (Aug 24, 2011)

Subject: In-line Truck Engine Misfire at Idle

Models: 2005-2007 Buick Rainier
2006-2012Chevorlet Colorado
2005-2009 Chevrolet Trail Blazer
2006-2012GMC Cayon
2005-2009 GMC Envoy
2006-2010 Hummer H3
With 2.8L 2.9L, 3.5L, 3.7L, 4.2L Inline Truck Engines (RPO's LK5 LLV L52 LLR LL8)

This PI was superseded to update model years, engine RPOs and recommended field. Please discard PIP4013B.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
On rare occasions, a SES light and P0300 DTC may be encountered as a result of single cylinder misfires only at idle. These misfires may or may not be felt and they will disappear off of idle. If the engine misfires do not occur at idle, this PI does not apply.

Recommendation/Instructions:
If the SI diagnostics do not isolate a cause for this concern, perform a cylinder leakage test as outlined in the "Cylinder Leakage Test" procedure in SI and document all leakage rates on the repair order. When performing the cylinder leakage test, it is very important to hold the crankshaft with the related piston at top dead center to ensure that the valves are fully closed or inaccurate results may be obtained. If an aftermarket leak-down tester is used, the instructions of the aftermarket tester should also be referenced because with some aftermarket testers, it may be necessary to limit the air pressure to 50 PSI in order to obtain accurate test results.

If a leaking intake valve is found, replace the cylinder head and valves by following the latest versions of 07-06-01-018 (LL8 4.2L), 06-06-01-017 (RPO’s L52, LK5) and 07-06-01-019 (RPO’s LLR, LLV).

Important: Before replacing the cylinder head, review the latest version of PIP3940, which contains some tips for using the lower timing gear tensioner holding tool (EN48464) described in the latest version of the above bulletins. These bulletins contain a revised cylinder head replacement procedure that no longer requires removal of the oil pan, front cover, water pump, or crankshaft dampener. Also, as mentioned in the above bulletins; it is important to install the cylinder head before you install the camshafts. Once the head is installed, the J44221 (Camshaft Holding Tool) should be used to hold the cam flats as the camshafts are installed with the #1 piston at top dead center.

Note: If the cylinder head is installed with the camshafts in place, without using the J44221 to hold the cam flats, or without the #1 piston at TDC, one of the valves could bend, resulting in an engine misfire at idle once the repairs are complete. As a result, it may appear that the new head has the same concern as the cylinder head that you just replaced, when it is actually the result of a bent valve.
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Old 04-30-2012, 01:41 PM
uga06dawg uga06dawg is offline
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Ok great! I changed the plugs this weekend but that didn't help. They were definitely in need of changing though. It's really just more aggravating than anything. Thanks for your response!!
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Old 05-01-2012, 12:08 AM
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petevw petevw is offline
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When was the last time the throttle body was removed from the engine and cleaned?

Do a search on this forum for "cleaning the throttle body"....you should find a sticky thread that explains how to do it correctly.

Also, what brand and # plugs did you put in the engine?
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Old 05-01-2012, 12:27 AM
onewheeldeal onewheeldeal is offline
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If your service engine light is not on, I'd say the vibration your feeling is worn motor mounts. I would have them checked.
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Old 05-01-2012, 08:29 AM
uga06dawg uga06dawg is offline
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Pete - I don't know the last time the throttle body was cleaned. I will look into that on the forum. I uses Delco Iridium plugs.

OneWheel - The vibration is only slight and it does not do it once the engine has warmed up real good.
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Old 05-01-2012, 10:59 PM
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petevw petevw is offline
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Quote:
Originally Posted by uga06dawg View Post
Pete - I don't know the last time the throttle body was cleaned. I will look into that on the forum. I uses Delco Iridium plugs.....
Delco 41-103's are correct ones.

Let us know how you make out after doing the tb cleaning.

And DON'T forget to remove it completely from the engine and have the battery disconnected the entire time (35-40 minutes minimum).
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  #10  
Old 05-07-2012, 06:32 PM
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Ostrandr Ostrandr is offline
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02 LTZ 4.2i6

Somehow i am going to try and get this rough idle problem figured out.

So far had a p0300 code random/multiple cylinder misfire detected so i decided to change plugs and cleaned the throttle body. Got that done and got a misfire on cyl 5 so i changed cyl 5 with cyl 3 coil pack cleared code now have random/multiple cylinder misfire code again so i put new coil pack in cyl 3 (just to make sure) and still rough idle.

is there anyway the rough idle could be something with the exhaust or my luck would it be something electrical
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