View Full Version : rough idle and hard shifting

08-11-11, 08:12 PM
i have an 07 sts that idles rough at idle. i have been to the dealership and the can't find a problem with no check engine light. i was also having problem with rough shifting and they fixed it with software update but it is starting to come back. has anyone had problems like this???!!!!!

08-11-11, 11:38 PM
I had a similar issue. My STS was stored in the garage at night and the next morning, I would start the car and it would idle rough with dark smoke coming from the exhaust. Cadillac has a technical bulletin for these cars in the cold weather invironment. I don't have the bulletin # through GM written on my invoice but its a start. Contact your dealer to see if they could assist you.

08-12-11, 09:28 AM
was this all the time or only when it was cold out? mine does it no matter what the temp. is

08-12-11, 06:10 PM
Oil level full?

08-12-11, 09:36 PM
oil was full . it is a v6 . i have tried every thing . high test gas makes no difference either

Dj Brady
08-13-11, 01:09 PM
Rough running conditions and dark exhaust smoke can be faulty O2 sensor causing a rich situation. You can confirm this with a live data scanner and if this is the case, fix it before it toasts the Catalytic converter (in the affected side of the engine).

Other rough idle issues can be from vacuum/intake leaks. if you're mechanically inclined, spray a little ether around the intake starting at the snorkel behind the MAF sensor and ending around the base of the intake. If you hear a change in the idle behavior while spraying, you've got a leak somewhere.

Of course, as software driven as these cars are, it could be a computer/programming issue, but that seems to be unlikely (but not unheard of), which would, most likely, require the proprietary computer (Tech-II or compatible) to read computer functions while the car is running.

Good luck!

08-13-11, 03:29 PM
don't have any black smoke. i think it is a sensor , but untill it fails i don't know what else to do.i think i will check for vacuum leak just to rule that out. thanks to all!!!

Dj Brady
08-13-11, 04:14 PM
yeah, I saw the lack of black smoke in your issues after I posted. I kind of threw that in there "just in case" since the second post listed that as a symptom.