Rough Idle.... Still

[bajamcguide]

Trying to figure out the low? rough idle on my 06 H3, with the I5 3.5 with about 85,000 miles

Little history, purchased new from Southbay Hummer in 06, at 17,000 miles the dealer replace the cylinder head
all good till about 70,000 miles, when I saw blue/white smoke at start up after sitting for few hours at work, no CEL, but the motor would idle too slow and almost die at stop lights.
Removed and cleaned the throttle body and cleaned the MAF sensor, and the motor ran fine for about 2 weeks, Then the motor started to idle rough, I replaced all the spark plugs, and noticed that 2 of the plugs
were wet.
Back to dealer,they did a leak down test and found 2 cylinders bad,I had to fight them to get the price down to $1200 dollars to replace the cylinder head.
after 1 week I picked up my hummer,now on its third cylinder head, drove the car of the lot and had the exact same problem, low rough idle..retured to the dealer immediately to show the service manager the problem.
He said he didn't know what was wrong, but he was sure they needed to replace the head based on the leak down test. All the techs were gone till Monday, so he told me to come back on Monday, and they would do some diagnostic test to find the problem.

I have lost faith in that dealer, So I took the Hummer to Tustin Hummer and explained the problem. They told me the factory recommended that they disconnect the after market radio, and re flash the computer.
so when I picked up my Hummer the radio was connected and the motor was a little smoother, and the idle was at about 700 RPM's
fast forward 6 months and 5,000 miles and the motor is back to slow( 600 RPM) and shaking.
I am now living in Utah, and I am trying to fix this myself.

so far I have changed out the following. the MAF, all the spark plugs, the cam position sensors, the cam timing actuator, I replaced the #1 coil ( also moved the other known good coil packs) ran about 3 bottles of
injector cleaner.added Seafoam to a tank of gas.
Anyone have any more Ideas?

 

[H3slate]

Is it rough only at idle? When you accelerate does it go away? I had a loose intake manifold that was causing those symptoms with no CEL.

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[bajamcguide]

anything above idle is fine. Sometimes if I turn on the AC the idle increases a little and the engine seems smother. also notice that it is rougher in colder weather.

 

[hummech]

does the vehicle have any codes stored in it? normally when the head has a issue it has a check engne light on. the problem that they had with the heads was the valve seats were moving down into the head and the valve could not seat against the pressed in seats. if this happens it throws engine misfire coads. if you want to eliminate the head as the problem, do a quick compression test and see where all the cyclinders sit. if they are fine, you could have a small vacuum leak.

hummech

 

[bajamcguide]

still had the rough idle right after the dealer installed a new head, so I think( hope) the head should be ok. I looked around and could not find many vacuum hoses. I sprayed throttle body cleaner around the intake and could not detect any leaks. Are there any other places that could be loosing vacuum?

 

[amrg]

Im currently getin my 3 serviced. I complained about a rough idle, dealer cleaned the throttle body and i quote "had a tech reprogram the throttle body door so that it opens/shuts properly and at the correct location"

 

[bajamcguide]

please let me know if this solved the problem. I am ready to try anything

 

[amrg]

Btw have you checked ur engine mounts? Usually they go out every 30k miles on my truck, they result in the truck vibrating at idle (making it feel rough) offcourse if ur truck feels like its gna stall at the moment then nevermind what I said

 

[digglesworth]

I too have a low idle... looks to be around 600rpm. my head was replaced at 32,000 as well. I have been noticing that the truck is "stumbling" a little bit at idle. it will be smooth and then its like the truck hiccups... ive never felt like it was gonna die but it seems to go through this in spurts... I was thinking maybe a coil pack was failing. keep us posted as to any fixes. I just cleaned my MAF and TB but it wasn't too dirty (just did it 10,000 miles ago)... ill try and check the intake manifold. mine also seems to be worse in cold weather.

 

[bajamcguide]

the CEL is not on, and I don't have a code reader( maybe I should). one strange I noticed today was when the hummer was doing its rough idle thing, I hit the electric lock switch and noticed the idle get rougher for
the spit second that the switch was activated. strange?

 

[alrock]

You can get an auto parts store to run a CEL check. As for the momentary dip in rpm / roughness that would be just from the alternator kicking in to the new electric surge

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[Mr_Rich]

You can get an auto parts store to run a CEL check. As for the momentary dip in rpm / roughness that would be just from the alternator kicking in to the new electric surge

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I noticed that the poster was from So Cal. My gf went to a local auto parts store for similar help and they told her it's against the law now. This being So Cal I wouldn't doubt that fact.

 

[digglesworth]

From what I've heard, they can pull the codes for you but can't reset the CEL light... I dunno if CA is different. Very well might be possible with all the regulations out there....

 

[Nevets1119]

the CEL is not on, and I don't have a code reader( maybe I should). one strange I noticed today was when the hummer was doing its rough idle thing, I hit the electric lock switch and noticed the idle get rougher for
the spit second that the switch was activated. strange?

Sounds like it could be a relay or cable problem, id check all your cables and connections see if any are bad.

 

[bajamcguide]

Ok tried to do the seafoam treatment through the vacuum line. slowly sucked 1/3 of a bottle into the vacuum port on the throttle body. I did not see a a lot of smoke coming out of he tail pipe, but I did notice a little puff of smoke come out near the rear of the engine on the exhaust side. could a loose or cracked exhaust manifold cause a rough/ buzzy idle? I did not think to look there as I would think the tech would have noticed that when the head was replaced.
I will remove the heat shied tomorrow and have a look.

 

[digglesworth]

Funny you mention exhaust. I started my truck the other day and noticed some exhaust coming out from under the truck by the passengers side door. It was a cold morning so you could see the exhaust. I tried peeking under there to see where it was coming out but did not visually confirm it was coming from the exhaust. It seemed to dissipate within a minute or two so I thought maybe I splashed some slush up there last time I pulled into my driveway and it was still a little wet under there... I'm curious as to the answer of your question.

 

[amrg]

please let me know if this solved the problem. I am ready to try anything

Just got my truck back and no more rough idle.

 

[bajamcguide]

AMRG... what was it that fixed the rough idle?

 

[amrg]

AMRG... what was it that fixed the rough idle?

Please check post #6

 

[bajamcguide]

got it thanks

 

[digglesworth]

Please check post #6

Do you know what that entails? Do I just go to my GM dealer and ask if they can reprogram the TB flap... Where does your truck idle. Mine is around 600... I don't want to pay the dealer to troubleshoot and charge me out the a$$ to tell me it "could be" this or that. Plugs were replaced 10000 miles ago with the ported throttle body... To me it seems like 600 is low... What should the I5 idle at?

 

[06PullUouT]

********WARNING: THIS IS A HONG KONG NO ****TER**********

I had a similar rough idle issue, to the point where it would almost die. I am mechanically inclined and ran over the whole engine with a fine tooth comb. I easter egged all the usual suspects to no avail. This was all during the winter time (in CT) so I never used the A/C. Well, spring and summer came around and it was time to turn on a little A/C when the Mrs was in the H3. Press the button.......... warm air. WTF! Finally broke down and took it into the dealer. After 10 minutes the tech came out and said that my expansion valve was clogged and cracked. Well, $76.99 and 1 hour and 45 minutes later I drove home with cold a$$ air and no more rough idle.

I asked how the hell the expansion valve made the truck have a rough idle and the tech said that the crack in the A/C line had allowed air to get into the system (no longer pressurized) which allowed "gunk" to get into the system as well. All this jacked with the compressor some how and bogged down the engine.

So at the end of the day all I know is I could barely keep it running at idle before they worked the expansion valve, after replacing it I haven't had one issue at idle!