I'll only claim to know some mere basics about superchargers but i claim to know nothing about GM superchargers, especially for the cobalt.

My boyfriend is interested in a used 2006 Cobalt supercharged, it's got 32,000+ miles on it and is reasonably priced. When we went to test drive it we pulled over in a parking lot to switch drivers to see if i could feel anything different with the handling of the car. When we were parked the car was while idling was shooting up to about 2k rpms and then it would drop down to just above 0 and the car would begin shuddering. Not wanting to stall out and possibly be stranded in the middle of St. Pete we drove right back to the dealership and told them about the problem.

We just now found out, after the dealer took it to a mechanic to fix the problem, that the previous owner had upgraded to the stage 2 supercharger (lightweight pulleys, flashed ECU, ect). The car is immaculate and very well taken care of but the shuddering when the car idles doesn't seem normal.

Neither of us having ever owned a supercharged car before and are pretty much noobs to whether the dealership is trying to pull a fast one on us by saying that the car is supposed to do that with all the upgrades on it or if they are actually telling us the truth.

Here's a link to the car:
View Inventory

Thoughts? Help?
Thanks in advance guys.

 

car will be fine once it gets to a tuner assuming the install was done correctly. it needs to be tuned!!!

 

i have to disagree. it does appear to have an aftermarket intake and a short throw shifter. notice they don't get a close up of the pulley. i have always seen the aftermarket pulleys an aluminum color and not black like the factory one. now i could be seeing belt or a black pulley but either way wouldn't you want to get an up close picture of that if it was a selling point.

also even the cars i have seen get the up grade levels their cars would still run fairly normal and idle normal before the tune. you shouldn't get the shuddering or a bouncing idle.

 

if the stage 2 is the factory gm then yes the pulley will be black. as far as the idle surge it sounds like the air pressure sensor took a crap. if you buy it id have them run a diagnostic on the car and have them fix it before you drive it off the lot.

 

Idle and driveability should be just like stock. There should be no surging or idle hunting. It might need to be tuned or something mechanical might be wrong. I would have them find the issue and fix it. If you buy it as-is you could be potentially opening up a huge can of worms...

 

agreed. the stage 2 tune is fine. as long as it IS the stage 2 tune. my buddy has a 06 SS S/C stage 2 and it runs just fine. even added a header and brought out more top end power. to be sure the pulley is a stage 2 pulley it should measure out to 2.8" stock they measure 3.5". Hope this helps

 

did your friend have to clean the throttle body regularly to keep it running properly? It seems like this is the answer we've found on a cobalt forum for the stage 2 mods. Apparently several people have had problems with there being 'gunk' accumulating and having to clean it.

The GM dealership seems to know nothing about this problem and claimed it could be solved by reinstalling the stock air intake....this obviously does not SOLVE the problem.

 

dollars to donuts the issue is either a vaccum leak or the MAP (Manifold Absolute Pressure) sensor has taken a dump. was there a check engine light? a check engine light will come up on many jap cars because of them tossing on larger intake systems because the MAF (Mass Air Flow) sensor is reading a larger volume of air then it knows what to do with. the MAP sensor will aslo do this if it is not registering a reading. it will read a static number (for instance on a 2000 impala with the 5v wire broken, it will read a static 31.96 inHg). I am really leaning towards something as simple as a vaccum leak though.

 

no he has about 20k on the stage 2 and never had a problem with it. throttle body is nice and clean. car has almost 50k on it now. he did have a problem however when he had an intake on it that it rubbed a hole in the piping. but thats it. reinstalled the stock intake and never had a problem out of it. also another thing i just thought of about the idle surge. make sure the vaccum hose for the boost regulator in plugged in. by taking it off you increase boost a couple of lbs. good only for running at the track. NOT for everyday driving. I have seen by leaving the hose off it can cause the car to surge.

 

Yeah, no check engine lights came on, the sensors were checked thoroughly, i believe they even installed new ones just to be certain and that wasn't the problem.

thanks for the help reiners88. we'll check the boost hose too. The mechanics suggested reinstalling the stock intake, hopefully it won't come to that. We're going to inspect it one final time before sealing the deal tomorrow, i'll post more questions (which hopefully won't happen)