Okay, so I did a search and didn't see anything about this so I figured that I would ask since my dealer doesn't know what this is....
I have an unusual shake that feels like it is coming from the front right tire. The tire is balanced, and the car has a good alignment. The car only shakes when I accelerate, or maintain a constant speed (like when I'm on cruise control). If I get off the throttle or turn off the cruise, the shake goes away. The dealer was kind of stumped, so they replaced the right front wheel bearing, but that didn't do any good. It hasn't gotten any worse, but hasn't gotten any better.
Any ideas?
Thanks!

 

this happened to me a few weeks ago, probably not your same issue but i had a little vibration front the front drivers side getting in upper RPMs in 1st & 2nd.
I checked my lug nuts, they were a little loose, so i tightened them & that solved my problem..
GL

 

CV Shaft/ Axle

Had that problem before with my old 1993 Dodge Shadow....
I know this is a Cobalt now, but some mechanical things are
universal.

 

Well, all the lugs are tight, I checked them and so did the dealer. And this isn't a little shake...if I leave the car on cruise around 70 the shake progressively get worse...and the whole damn dash shakes. And here is something else... when I go over a bump and the car rebounds when the suspension isn't loaded with the cars weight...the shake temporarily goes away. Are the shocks in these cars known for going bad? Think that would be it?

 

Id say check your CV Axles... Shocks MAYBE... If its been going on for a while, you might be able to see an abnormal wear pattern in your tire that could help. Im sure you can find a chart of tire were patters/malfunctions on google. Also check for a loose tie rod end, something doesn't seem to be very secure.

Get the front end off the ground and onto jackstands... Then lay under the car and move the wheels manually and listen/feel for anything abnormal.

 

Did they just put an impact on them? or did they Check them at 100' lbs with a torque wrench? OVER tightened lugs can also cause problems.... So try backing them off, then retorqueing them to 100 ft / lbs.

 

The dealer said that they checked all of the suspension and said it looked fine, and everything was tight. I told them that this car didn't have this shake before they did the recall on the power steering motor....

 

Have them test drive it with you....

Id check out the CV/Axels though... still a good possibiltiy...
Also get it up on jackstands and rotate the wheels through by hand.... listen/feel for any abnormalitys, See what happens if you let go of the wheel while its shakeing? does the wheel go leftrightleftrightleftrightleftright... or just kinda vibrate... try high/low/mediaum speeds... but make sure you can still maintain control...

My money is still on a CV Joint/Axle

 

100ft isnt that a bit much??for lugs

 

100 ft lbs is what the owner's manual says....

I think my old Shadow was like 90 or 95, I forgot,

But the GMC Acadia's lugs are 140 ft lbs...
So its not the highest I've heard of....

 

Hmmm imma have to look.im.used to hinds and its 80lbs I was just asking

 

possibly a clutch issue? like warped flywheel or pressure plate

 

Check out the control arm bushings