Sometimes the engine will vibrate at idle like it has an aftermarket cam in a gasser...

Wonder if its the exhaust just vibrating or what?

How much vibration do you get when you put your hand on the intake horn?

Shakes the truck a little...

 

The POWER of the CUMMINS

 

Could be ideling a little slow.....

 

Has it been the same since u owned the truck, or is it somthing new? All i can say is u'll never try to start a cummins while its running like I did my sisters honda civic when I drove it alittle while ago, lol. These things are loud especially with the hood open, and vibrate alot. Have u checked out the motor mounts it sits on? there huge.

 

Your idle is probably a little on the low side, idealy is should be 750-800rpm's with the A/C on. I know mine after towing a HEAVY load with the A/C on will lose 100-150rpm's than before I towed at idle.

 

See if your motor mounts are good and tight also.

 

You really think the motor mounts could be loose?

I'll check 'em...

 

And what are some tell tale signs if I can't find anything?

Kinda soon to bust a mount, eh?

It doesnt do it all of the time...

 

does the idle drop when it vibrates? or sputter at all?

 

I watch for it and it doesn't...

 

So yeah? Anyone else?

 

mine does the same thing but its cause idle is a little low but i think it looks kinda cool sittin there shakin side to side

 

check out your harmonic balancer; mine has the rubber all messed up and is "hopefully" going to wait for the new fluidampner to be bought before it shells out...

 

Change your fuel filters. I changed mine and it idles smooth now.

 

A ruff idle , like mentioned about the idle should be 850rpm AC on in gear .
Then check the valves for adjustment , thats a comin ruff idle cause .
When looking for problems I always look at the maintenance issues 1st , many times this will solve an issue , and may help to find an issue , when looking to solve a problem never go around unknowns ,
The last is that you said that it was not all the time , is it ruff when in gear and or AC - low idle .
If all above are good , it sounds like a fuel issue , try 10-20% bio-diesel [ this does a number of things , cleans the system better than anything , thats why those that do carry extra fuel filters , if not available , try 2cycle oil , both will make the eng. run quieter & smother at idle ,
I have been noticing that it seems that since the ULSD , that the fuel must very , same driving , & my millage will very by 1 1/2 - 2 mpgs .