My car is now back at the dealer this morning. This is my final effort to get them to do something. I'm expecting a call this afternoon with "no faults found - operating as normal!". Then things will get very interesting.

 

I was screaming vacuum leaks about 3.5 years ago and the dealer dismissed me.
No fault code = No problem..

 

Assuming the dealer does nothing, my next action is to take it back to the independent mechanic for a smoke test of the intake system to identify any vacuum leaks. $540 out of my pocket for diagnostic work that the dealer *should* be doing.

FYI - most of that cost is for labor of just uncovering the engine .

 

Just got an email from my SA that the regional tech rep told them to not do anything to my car until after he drives it & experiences it first hand -on Wednesday! No PDK valve body, nada! Car has been there a week, and all that has been done is PDK oil change and all the updates verified. Evidently he read the tech-line info from the mechanic and isn't "buying" it! I'm starting to think 997 TT Cab now! Stay tuned 😳

 

Maybe it'll be the same regional tech rep who told me I was driving it wrong.

 

I got a late afternoon email yesterday that said "we installed the valve body and it didn't fix it"! Duh! My SA said the rep could not come back today so they are waiting for further instructions from him. He also said the rep is a "good guy". I have not heard a thing yet this morning. 11 days and counting w/o my beloved 911 but at least it "sounds" like the rep didn't like the way my car (hesitated/stumbled) drove. Stay tuned some more. The waiting is the hardest part (Tom Petty 1983).

 

Indeed. My car has been in since Monday morning and they are still working on it. Hopefully this means they are actually doing some diagnostic work this time!

But the wait is ok... got to drive the '86 911 in to work today .

 

wish I still had my '86 Targa!
The SA just told me they are now switching out the Mass Air Flow sensor! Waiting for the testing result! Possible issue?

 

Apparently they utilize the renowned method of trial and error to diagnose our cars.
Amazing what happens when you replace mechanics with technicians.
A sad state of affairs..

 

If your scenario comes to pass and your indy fixes it, you should send the bill over to Porsche. No reasons you should be out $540 for a issue Porsche cannot fix but an indy can. Damn, that would be embarrassing.

 

Exactly my plan. You better believe Porsche is getting the bill.

It seems like the dealer and/or PCNA has no desire to do actual investigative work if there are no error codes thrown. Everything is up to the computer now. Nobody wants to get in there and start looking around.

 

I've been thinking about getting a used 991, however, this stumbling issue is a concern (I can imagine someone trading in a relatively new car due to this issue).

Is it easy to reliably detect the stumbling issue on a testing drive? How consistently does it occur?

Thanks!

-dbk123

 

[QUOTE=stealthboy;4633194]...

"Check over car, test drive to experience customer complaint. Found rough idle and stumble with light throttle at 2800 RPM. 3rd gear. Check car with scanner read out fault memory (all OK). Check live data, found fuel trim at idle off bank to bank by 1% (should be closer). Recommend check of intake system sealing. Possible vacuum leak."
...

Interesting. My car has similar symptoms, stumble, no codes, etc. I was able to collect some data via the OBDII connection and looked at the fuel trim data over a 13 minute drive. There are both long term and short term fuel trims on each bank. Here's the differences (Bank 1 - Bank 2, %) that I found:

____ Long Short
Min. -3.13 -10.16
Ave. -0.84 -0.85
Max. +0.78 +9.38

The same data only at idle:

____ Long Short
Min. -2.34 -4.69
Ave. 0.00 -1.11
Max. +0.78 +1.56

The Min and Max values may be of more interest than the Average since the car does run smoothly some of the time. I'd love to see the same parameters on a car that DOESN'T have our problem.

 

DBK, I'd like to say that "yes" it is easy to differentiate between a 991 with the stumble issue & one w/o it. Truth is, it doesn't happen often or frequently (that's a good thing). But if you drive it for at least 30 mins with these parameters, I think you will know: sport mode, form standing stop, accelerate moderately to attempt to get the PDK to shift around 3k rpm. For a manual, I assume you need to rev it to 2800-3000 before shifting. If it stumbles/hesitates, you will feel it! It is a rarity too. The car is awesome otherwise. Hope this helps. GL.

 

Don't let this ruin every 991...
Have it checked out, like a normal sane person.
You or someone familiar with this issue, or someone knowledgeable about Porsches.
Mine has no problem...and every 991 owner I speak to does not have it.
I attend lots of cars Coffee, and am a PCA Member.
Some have never even heard of it.
It's overblown.
Just check the car out.