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  #1  
Old 01-29-2010, 10:49 AM
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Cold Air = Rough Idle

I was working on a rough idle several days back. Replacing old vac hose I thought stopped it, but I think the weather just turned warm at the same time. Now the temp dived again and the rough idle is back.

It acts like a vac leak. How could cold cause this?
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  #2  
Old 01-29-2010, 02:53 PM
JMC JMC is offline
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When the temperature gets colder parts contract. After the engine warms up does the rough idle go away? A loose clamp or hose may loosen further when cold.

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  #3  
Old 01-29-2010, 10:05 PM
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the problem does get better as the engine heats up
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  #4  
Old 01-30-2010, 09:28 AM
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I'd say clean your IAC on the back of the throttle body elbow- looks like a silver electric motor can with a plug on it. Clean that, throttle body and MAF sensor to see if that helps. Otherwise, those things are good to do anyways.
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  #5  
Old 01-30-2010, 02:45 PM
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already tried

Have replaced IAC, cleaned MAF, replaced small vac hoses, retightned clamps on TB pipe, replaced PCV valve.

In addition I have also called it ugly names and kicked the tires a few times. The latter did not help, but I felt much better afterward.

It's the cold issue that confuses me. I wonder if there could be a crack in somedthing that opens in the cold and closes when warmer.

Quote:
Originally Posted by BLUE20004X4 View Post
I'd say clean your IAC on the back of the throttle body elbow- looks like a silver electric motor can with a plug on it. Clean that, throttle body and MAF sensor to see if that helps. Otherwise, those things are good to do anyways.

Last edited by dburgjohn; 01-30-2010 at 06:00 PM.
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  #6  
Old 01-31-2010, 09:23 AM
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I've never experienced it (yet) but maybe a plugged EGR? Pretty sure a code would come up pretty quick for this though. How are the spark plugs? Fuel filter? injectors? I'm at a loss, just fishing!
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  #7  
Old 02-01-2010, 12:33 PM
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A vacuum leak will cause your symptoms. Cold engine, start it and using carb cleaner spray all the vacuum lines and intake manifold joints. When the idle changes you have found the leak. According to the year of your truck you have a composite intake manifold. The odds are that it is leaking where it connects to the heads.

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  #8  
Old 02-09-2010, 07:39 PM
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cold manifold

can a intake manifold leak only show up in very cold weather, then go away when it warms up?

Quote:
Originally Posted by JMC View Post
A vacuum leak will cause your symptoms. Cold engine, start it and using carb cleaner spray all the vacuum lines and intake manifold joints. When the idle changes you have found the leak. According to the year of your truck you have a composite intake manifold. The odds are that it is leaking where it connects to the heads.

Regards

Jean Marc Chartier
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  #9  
Old 02-15-2010, 10:21 AM
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temp down

the temp dropped from 40's to 25 and the miss at idle came right back. I can't find this stupid leak
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  #10  
Old 10-09-2011, 04:16 PM
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after the summer

after a summer of running perfect the temps have dropped again and the miss is back. feels like my options are:

A) Someone here gives me a awesome idea of where to look
B) I move to the Gulf Coast
C) I shoot it

hopeing for options A, not sure which of the others I would prefer
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  #11  
Old 10-09-2011, 04:20 PM
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Quote:
Originally Posted by dburgjohn View Post
after a summer of running perfect the temps have dropped again and the miss is back. feels like my options are:

A) Someone here gives me a awesome idea of where to look
B) I move to the Gulf Coast
C) I shoot it

hopeing for options A, not sure which of the others I would prefer
Weather has absolutely nothing to do with it. Thought I would let you know.
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  #12  
Old 10-09-2011, 04:25 PM
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What is your exact idle rpms cold and @ operating temp. You have to be precise if you want correct info. So write it down, next time you think of it.
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  #13  
Old 10-09-2011, 08:14 PM
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check the IAT and EGR . either could cause this problem
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  #14  
Old 10-10-2011, 05:57 PM
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When the outside air temp drops below 50, the idle bounces from 300 to 700 every one to two seconds. When the temp is above 50 it sits rock solid at around 650. When the outside air temp is around 50, warming the enging up will make the rough idle go away. When the outside air temp drops into the low 40s or 30s, the rough idle is there not matter how long the engine has been running. You have to use both feet at a stop light to keep it from dying. Off idle it runs great not matter what the engine or outside air temp is.

Quote:
Originally Posted by jbrew View Post
What is your exact idle rpms cold and @ operating temp. You have to be precise if you want correct info. So write it down, next time you think of it.

Last edited by dburgjohn; 10-10-2011 at 06:07 PM.
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  #15  
Old 10-10-2011, 06:41 PM
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A couple of other things to look at are your maf and thermostat.....
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Old 10-10-2011, 06:41 PM


 
 
 
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