Rough Idle When Cold

[UMEXT]

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]

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]

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]

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.

 

[The_Roadie]

Motor mounts.

 

[JerryIrons]

Also have you cleaned your throttle body lately ?

 

[WarGawd]

Motor mounts.

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

 

[The_Roadie]

...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 - - -

Also have you cleaned your throttle body lately ?

Throttle body was ruled out by the answer in post #4.

 

[WarGawd]

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]

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]

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]

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]

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]

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]

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]

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.