Rough Idle When Cold

UMEXT

Original poster
Dec 16, 2011
110
No codes set, no lights turned on, smooths out beautifully once the engine is up to operating temp, just started yesterday. Any ideas as to causes/solutions?
 

TangoBravo

Member
Dec 5, 2011
208
MANY, could be CPAS going out, could be the cam actuator it's self(unlikely), could be the CAT, could be cam sensor, could be crank sensor. Yes most all if these should set codes and lights but mine didn't for a long time. Mine still does this and the only thing I haven't replaced yet is the cam actuator it's self.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Describe the roughness precisely, please. Can you feel it go up and down and see it on the tach? Or is it a 10 Hz vibration that's worse in DRIVE than in NEUTRAL?
 

UMEXT

Original poster
Dec 16, 2011
110
the roadie said:
Describe the roughness precisely, please. Can you feel it go up and down and see it on the tach? Or is it a 10 Hz vibration that's worse in DRIVE than in NEUTRAL?

The latter.
 

WarGawd

Member
Sep 2, 2012
468
the roadie said:
Motor mounts.

UMEXT said:
No codes set, no lights turned on, smooths out beautifully once the engine is up to operating temp, just started yesterday. Any ideas as to causes/solutions?

Roadie, for my benefit and for potential future readers can you explain a bit more about how you zeroed in on the mounts given the sudden appearance of his symptom and the connection to it's disappearance at normal temp?

Thx :smile:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
WarGawd said:
...can you explain a bit more about how you zeroed in on the mounts given the sudden appearance of his symptom and the connection to it's disappearance at normal temp?
Long experience, and I had the issue myself. To check more of the history, I recommend a site-restricted search like this at Google "motor mounts site:trailvoy.com" or the same kind of search here.

Here's my classic thread on the subject: [SOLVED] Bad vibration in gear at idle solved by new motor mounts - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

- - - Updated - - -

JerryIrons said:
Also have you cleaned your throttle body lately ?
Throttle body was ruled out by the answer in post #4.
 

WarGawd

Member
Sep 2, 2012
468
the roadie said:
Long experience, and I had the issue myself.

<snip>.


Thx roadie....I guess the part I was looking for even more and can't grasp ATM was how the nomal operating temp gives rise to to a reduction/elimination of the vibration - I scanned the referenced thread, but didn't see it discussed??
 

JerryIrons

Member
Dec 20, 2011
434
Well metal usually expands as it heats, so it must expand out enough so that there isn't room to vibrate? Thats the only thing I can think of.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
It's involved with the elastic stiffness of the collapsed mount. Not related to metal. 600 rpm = 10 Hertz. It's a rotational resonance that GM engineers failed to model because they didn't predict collapsed mounts.
 

jeffro312

Member
Oct 4, 2012
442
East Haven,Ct
while were on the question of motor mounts sorry to hijack not my intention..... any specific brand or motor mounts should be used? any recomendations where to get them. is rockauto,com a good site?
 

TangoBravo

Member
Dec 5, 2011
208
jeffro312 said:
while were on the question of motor mounts sorry to hijack not my intention..... any specific brand or motor mounts should be used? any recomendations where to get them. is rockauto,com a good site?

I like rockauto I use them all the time. As far as brand I don't know which would be better, as a general rule I try and stay away from brands I don't know. If rockauto doesn't have what your looking for try gmparts direct I have had good luck with them as well.
 

jeffro312

Member
Oct 4, 2012
442
East Haven,Ct
TangoBravo said:
I like rockauto I use them all the time. As far as brand I don't know which would be better, as a general rule I try and stay away from brands I don't know. If rockauto doesn't have what your looking for try gmparts direct I have had good luck with them as well.

Thanks for input tango.... unfortunatly there are alot of brands i do not know about. just wasn't sure if its one of those parts that nobody can replicate like the auto trak 2 fluid kinda deal thanks again
 

Sparky

Member
Dec 4, 2011
12,927
OEM are the only ones that are recommended. However I think someone found that one set of aftermarkets are finally made correctly, but I'm not sure which ones those are.
 

neelskit

Member
Dec 7, 2011
69
the roadie said:
It's involved with the elastic stiffness of the collapsed mount. Not related to metal. 600 rpm = 10 Hertz. It's a rotational resonance that GM engineers failed to model because they didn't predict collapsed mounts.

When the temps dropped here in Indiana for the first time a few weeks ago, I discovered my bad mounts. On cold mornings, the vibration is substantial, on warm mornings or after the temps are above 70F or so, vibration is gone.
 

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