Have an 06 CTS-V bought new with 75 miles. I noticed it idled rough right from the start. Service said to break it in for a few thousand miles and it will smooth out. Not a chance. At 3K miles service suggested I run "top-tier" gasoline and it will smooth it out. Cheap gas is causing the problem. Not a chance. Now at 4K miles after having the sales manager sit in my car to feel the rough idle the service manager finally admits the rough idle is a misfire and there's nothing they can do about it since no codes are being picked up. They also said if I bring it somewhere to dyno it and correct the air:fuel mixture problem it may void my warrany on the drivetrain. Service has also said every single CTS-V they have been in idle's rough like mine. BS. Is there anyone else out there with this problem? I'll probably go to another dealer and see if they can straighten out this annoying problem. Thanks for any responses.

 

Hello i have an 03 deville also with rough idleing it only has about 34,000 miles and i can't figure out what the problem might be. I don't know if these situations are related or not?

 

That is ridiculous. They don't need a code to figure out the misfire. All they have to do is hook up their engine analyzer and it will tell them which cylinder(s) are misfiring. Obvious problems to look at, spark plugs - how hard is it to pull 8 plugs and look at them, Coils and fueland air filters are other easy places to look. Another idea is to take it to a Chevy dealer with Vette experience, can't see how another GM dealer will void your warranty.

On the 03 Deville see above and start easy, fuel filter, air filter, plugs. I had a plug crack in my Deville and GM said that was rare but who knows. The car ran rough at idle that's for sure, but once that cracked plug was replaced...presto, smooth as silk.