: stumbling problem at highway speeds...no codes

12-16-11, 01:48 AM
hi all , i own a 05 sts 4 awd 4.6 northstar...i got the car with 17000 miles on it. was dealer serviced from new til now.it is off warranty and now im footing the bill for all repairs.the problem im having started 2 years ago when i would approach a hill or mountain the car would stutter, buck but no misfire... brought the car in they couldnt find anything wrong...well now it does it on flat roads around 45-60 mph and i dont even want to drive the car.it has passing gear and when i put my foot in it she goes but i have to play with the pedal to avoid the stumble..i had caddy do a full 100000 tune up at 85000 and they replaced everything...still there the car has 107000 ,and most are highway miles ,on it now and they changed the mass air flow sensor, map sensor and reprogrammed the tcm.what i dont understand is why would the service writer let the car leave knowing they didnt fix the problem when he told me the car was 90% better and it is not...you pay 56,000 dollars for a car that the dealer cant fix..hopefully someone can shed some light on this thanks vinny

12-17-11, 06:53 PM
Does the Check Engine Light come on?

Many members have reported loose intake manifold bolts on the V8's. If the light comes on, there will be diagnostic codes stored to help the tech fix the issue. No light; no codes and such loss of power/odd troubles may be the result of loose bolts.

12-17-11, 08:56 PM
I would agree that the intake maifold bolts are something to consider. It may not be related to this at all, however I have two cars ('04 Bonneville & '08 STS) with the Northstar. Both had at least a couple of very loose bolts and none tightened to spec. There is a thread here on the forum about this. I can't recall anyone who posted stating they checked only to find there was no problem. This may be a very good starting point. I did post a torque spec in that thread, along with a tightening sequence. Unfortunately, the search function is not allowing me to find the thread.

12-18-11, 04:39 AM
It could also be a condition of the transmission. If the TCC (transmission converter clutch) is slow to disengage it could be indicated by a stumble, however this is just an alternative (possible) solution, and a vacuum leak causing a temporary lean condition (as alluded to in earlier posts), may be the culprit.

12-20-11, 12:34 AM
thanks for the info guys...went to the shop on monday and after work brought the car in to check the intake bolts...all were tight...what next check for a vacuum leak...caddy said they cant find any ...thats what i told them to check for ...they found nothing...should i call detroit...maybe get a rep. to look at it....very frustrating because the car is so nice but it drives like garbage...my 96 runs better...

12-20-11, 01:15 AM
So one of the tools that GM has available for intermittent problems like this is a diagnostic data recording tool. This plugs into the OBD-2 port. You activate it when the car is started and then when the symptoms occur, the operator will press a big red button on the top of the unit. The system will take a snapshop of various system parameters for several seconds pre and post button push. Once you have a couple of occurrences, the tool is returned to the dealership. The data is analyzed to try and determine what is occurring at the time of the actual symptom. This isn't a first line approach, but with intermittent problems when all other techniques have failed to identify the problem, it is an available option.

From what you're describing, it sounds like the dealership has checked a number of likely suspects. This diagnostic tool may be something you can discuss with the service department.

12-20-11, 09:56 PM
Intermittant problems are the most frustrating. And no codes to help either. Sheesh.

You have paid a lot of money and for the problem to not be fixed is unacceptable. Cadillac owes you a solution. I would take it back to the dealer and take the issue up the management chain. They need to reach beyond their local staff that has taken your money but not solved the problem. They have resources available with the manufacturer that can think beyond that normal course of action.

You mentioned that the dealer said it is 90% better. Do you agree with that proclamation?

12-20-11, 10:13 PM
Sounds like what Cadillac calls "chuggle." It's a symptom of a torque converter problem in AWD V8 STS's. Search the forum or Google for it.

12-21-11, 02:41 AM
thanks all for the replies..... the car is the same when i brought it in no different...it is definitely not 90% better,thats what pissed my off ...why would you release the car knowing the problem is not solved...the one tech said it feels transmission related and the car was reprogrammed twice (tcm) likes it shifting in and out of overdrive...i complained about this 2 years ago and they claim no miss was detected...obviously they dont know what the are doing because this couldve been done under warranty...i had them change the trans fluid and the tranfer case as well...now i cant even sell the car because it runs terrible on the highway. and to trade it in when im ahead on payments and have 3 left is crazy...i like the cts coupe but i will not trade down as far as options so your talking 50,000 to replace what i have...and i cant lease because of mileage...this sucks....vinny

01-05-12, 07:54 PM
ok ...here is the final prognosis..took the car back to caddy to look further into the problem. and now the tell me it is the torque convertor...two years later and out of warranty its going to cost me 3100 dollars...now work with me guys on this....do you think the dealer should be resposible for this repair..do i have any chance of calling detriot to get some relief on this....2 f#@king years and many dollars later they can finally fix the car...or we shall see...cause if on tuesday its not fixed after i pick it up you'll all be reading about an sts being driving right thru the show room floor.....did anybody have this problem and does this figure sound right...and should the trans be changed as well..they say no isay they're full of shit...

01-05-12, 08:15 PM
If you have a work order for the issue while the car was under warranty and it was never resolved, it's covered. You may have an up-hill climb to get it covered but the 'chuggle' is a known issue. You have a valid position.

01-05-12, 09:55 PM
Common problem, theres a ECM/TCM calibration update that band-aid fixes it. Had it done then continued they replaced the converter, here I am almost a year later and its doing it again. Taking the car in again to have them look at it.

You have to ease into the gas and sometimes it will still do it. Most times you cruise feather the gas to maintain speed it shudders, coast down a hill as the car slows it shudders go to pull up a hill ease on the gas and press down further to pull the hill sudder hahaha it always feels like its clunking in the rear end...

01-06-12, 05:30 AM
If you can't get it resolved under an old complaint (that was never rectified), then I think I would take it to a national franchised transmission shop. Most certainly they would be able to repair for less; and I'm thinking a lot less.

01-08-12, 01:16 PM
trans needs to be updated (flashed codes) and they should check ALL the PCV for cracks and leaks.