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Rough Idle


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#1 bam2880

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Posted 11 July 2011 - 05:38 PM

i have a 2008 gmc sierra 5.3 vortec with AFM and it idles kind of rough and when i put the hood up it kind of shakes a little bit but nothing major what could it be

#2 semper

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Posted 14 July 2011 - 04:22 PM

I have the same problem. I recently bought a 2010 Silverado with the 5.3 and it idles rough sporadically. It's very annoying. I got rid of a 1999 S10 with 200,000 miles that puured like a kitten. Now I have to deal with a $30k truck I've wanted for years unable to idle constant. Going to dealer this weekend for warranty request, from what I've seen online GM is dodging addressing any problem with the rough idle.


i have a 2008 gmc sierra 5.3 vortec with AFM and it idles kind of rough and when i put the hood up it kind of shakes a little bit but nothing major what could it be



#3 spock

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Posted 15 July 2011 - 06:03 PM

Join the club. My 5.3 runs great but the idle in park has some flutter to it that shakes the antenna. RPMs are steady. My 93 C1500 w/305 idled so smoothly you might not think it was running.
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#4 jro909

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Posted 16 July 2011 - 12:54 AM

vortec v8s idle rough....its from the computer leaning out the mixture...mine does it and probably 90% of other peoples do, its nothing to worry about unless your rpms are bouncing
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#5 semper

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Posted 18 July 2011 - 03:49 PM

Yeah my RPM's fluctuate also, you can watch the tach dance from 500 RPM then shoot up to 700 RPM and back and forth. Bad thing is my SES light isn't coming on so to the dealer nothing is wrong. It seems this has to be an issue with others. Besides that the truck runs flawlessly.

vortec v8s idle rough....its from the computer leaning out the mixture...mine does it and probably 90% of other peoples do, its nothing to worry about unless your rpms are bouncing



#6 jro909

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Posted 18 July 2011 - 11:06 PM

you got a cold air intake or any after market mods?
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#7 semper

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Posted 19 July 2011 - 06:53 AM

Nope, stock as can be. It does it pretty regularly, it's not horrible but enough you can feel it in the cab. I can sit and watch the tach fluctuate. It will sit at about 500 RPM then bounce up to 600-700 RPM then back down. It's very random. But does it with or without AC on and more in gear than idleing in park. I'm not getting and SES thrown so I have a feeling the dealer won't know what to do. It runs great besides that, just aggravating when I got rid of a 1999 S10 that purred like a kitten at idle. I would figure this has to be somewhat common with other trucks?

you got a cold air intake or any after market mods?



#8 JdubUB

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Posted 19 July 2011 - 10:16 AM

my truck runs good and strong, but in park it does idle rough. The truck will move, but the RPM's will not. It's just another "characteristic" of these 5.3 Vortecs
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#9 mkelly

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Posted 19 July 2011 - 11:38 AM

Add mine to the list, it idles rough once its warmed up.


I have noticed that If I get on it after a stop light it will idle smooth at the next stop light..... It will also idle smooth after I get off the interstate running at 75 or so.


I've seen this out of all of the newer 5.3s, but did not see the problem in the 5.3s from 99-05 range. I read somewhere that the newer programming dropped the idle very low to save fuel and thats what causes the problem.

#10 tgprince

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Posted 11 December 2011 - 05:02 PM

i have a similar problem with my 2006 sierra. its not throwing any codes but at idle it fluctuates 500-700 rpms. also when i let off the break and let it coast forward it it jerks the truck, not terrible but enough to be annoying. i tried new plugs and wires but no luck. once i get on the gas the truck runs smooth and strong. it only does it when the truck is warmed up and the rpms drop. any ideas?

#11 lonestar angler

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Posted 14 March 2012 - 11:47 PM

Same here with the rough idle. Worried I will be wasting my time at the dealership without an engine light on.

#12 JustinB

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Posted 15 March 2012 - 06:40 PM

My '08 does the exact same thing as well. I started noticing it shortly after I purchased my truck. I noticed it because it shakes the truck. I can even feel it in the door panels.

I did a lot of searching and reading on the subject, and it seems like a fairly common issue with these trucks. I actually started getting a CEL (P0121). I cleaned the throttle body and while it made a difference in the rpm fluctuation, it didn't help the stumbling/stuttering/shaking issue. Before the TB cleaning, the rpms would fluctuate like the engine had a slight misfire or hesitation. It appears to idle smoothly now by looking at the gauge, but sometimes the stumbling/shaking issue can feel pretty bad.

I swear it almost feels like bad motor mounts. However, I haven't gotten a chance to take a look at them yet. I previously owned an Audi A4, and around 86k miles, my front motor mount was worn completely out which caused almost the same exact sensation in the vehicle.

I've removed and cleaned my throttle body, removed and cleaned my MAF, checked all my vacuum hoses for leaks, checked around my intake tubing, box, etc., for leaks, and have came up with nothing to cure the problem.

I did read that some people had success with replacing the grommet on the brake booster. One guy even said that just removing and re-seating the brake booster vacuum line cured his problem. Maybe that could help you?

I'll eventually end up taking mine to the dealership and getting them to inspect it. My parents have always owned GM vehicles and I've owned a few myself, and never had a problem like this. You think when you pay that much for a truck that it would at least idle somewhat stable. The truck runs great when accelerating and such, but when I stop at a red light, it feels like the engine is stuttering almost to the point that I subconsciously want to give it gas to smooth it out. Maybe we should all start writing letters to GM about it, or calling and complaining?

Edited by JustinB, 15 March 2012 - 06:43 PM.

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#13 Doz El Dude

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Posted 15 March 2012 - 06:47 PM

I've got a 5.3 2011 and haven't had this problem. :dunno:




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