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Alrighty ladies and gentleman...the results are in!!
Replaced the engine mounts, went for drive, and besides making the ride back to
smooth because they were bad, it did nothing in helping the stumbling issue.
However...new BOSCH Throttle body solved the remaining 5-10% of the stumbling issue. If you watch the video above, I think the TB just flat out gets used up and the contact points become worn out.
The 991 drives so smooth now. This might sound weird but, the overall idle, exhaust note and behavior of the car is enhanced and is a joy to drive once again. Could it be just one or the other, possibly. But both were bad in my 991.
The gas pedal is the easiest to do followed by the TB which is not bad at all, just a lot of items to undo to get to it properly.
Hopefully this helps out others in the same boat.
New Bosch TB $150-180
New/used gas pedal $90-300
Result = Priceless
As an added bonus, you may also notice that my 991 S has an IPD intake! Cha-ching Never noticed that until I had it apart.
Last edited by GermanCarFan1; 06-07-2023 at 09:19 PM.
Sorry to hear that. At the very least, you had a few quality weeks of enjoyment.
I'm expecting mine to revert to it's former self sometime soon.
As has been mentioned before, looks like the problem is buried within the ECU, and temporary fixes are soon undone. Most likely, the only solution would be
a re-flash from Porsche, and we all know that will never happen.
I asked him about the PDK redo / flash and if it was connected to a "stumble" or affects how the car drives. He said yes and the refresh should take care of it...?
The only thing is that this happens on both manual and PDK, but looks like more PDK cars are affected.
Hopefully mine stays away, fingers crossed.
My appointment is next Wednesday, so I'll press him for any further details on this issue.
Sorry to hear that. At the very least, you had a few quality weeks of enjoyment.
I'm expecting mine to revert to it's former self sometime soon.
As has been mentioned before, looks like the problem is buried within the ECU, and temporary fixes are soon undone. Most likely, the only solution would be
a re-flash from Porsche, and we all know that will never happen.
I suspect you could be right. I am not giving up hope yet, though.
I filled up with Esso 94, a fuel I never run, and the symptoms only popped up after that (could be coincidence of course)
I'll drive to near-empty and fill with Shell 93, which is what I normally run
I'm going to inspect my throttle pedal and make sure the connector is seated properly. Entirely possible that breaking the tab has allowed it to wiggle loose maybe?
Also sort of wonder if the dynamic engine mounts failing could produce a similar sort of feel on/off throttle. My mounts are still original, I wonder if they're on the way out. I've had just about everything else in this car prematurely fail, so why not those, too? lol
I asked him about the PDK redo / flash and if it was connected to a "stumble" or affects how the car drives. He said yes and the refresh should take care of it...?
The only thing is that this happens on both manual and PDK, but looks like more PDK cars are affected.
Hopefully mine stays away, fingers crossed.
My appointment is next Wednesday, so I'll press him for any further details on this issue.
I'd gladly take the reflash if they had it for the MT cars. I hope that it helps you!
Sorry to hear...I only have the option of 91 octane here in AZ.
Just for reference sake, these are the items I've done just as basic maintenance when I first got my 991 and what I first thought the stumble was before I found this thread.
New plugs
New coils
New various cam sensors x2
Oil change
New Air filters
New battery
Since
New gas pedal
New Throttle body
NOS Dynamic PADM engine mounts $450 each - both on their way out
New transmission mount goes in tomorrow at my Indy - yes it was bad too
Well. My replacement pedal (donor car is a 2016 panamera with 35k miles) is installed.
I too broke the tab. I was gentle but I guess it had enough..
I used a small pick to lift up the tab from the other side and connector popped out. (why didn't I do this the first time: see this video
)
when the new pedal went back in, i heard it snap back in, so i don't think any issue there with secure connection.
drove the car around noon (upper 80s F) and I thought (placebo effect?) the stumble was a little bit better but hard to tell cause of road surfaces.
in the evening, it was a bit cooler (70s F) so I tried to do the throttle reset by turning ignition on for 30-60 secs...I didn't hear anything.
grabbed the icarsoft and went to ETC under service and hit reset. I heard the throttle body for a quick sec.
unfortunately, i still felt the stumble on the highway. maybe it's not as pronounced? I need to keep driving to really know.
@koala sorry to hear the stumble is back for you also.
are you going to try something next? seems like you have done everything. I am not even going to bother with the throttle body.
I remain convinced that it's in the DME.
Every time the dealer performed a s/w update or reset the DME, the car drove like a different car for 48 hrs and the power band was as smooth as silk.
After a day or two the stumble returned.
Oddly enough, ever since I moved to Europe with the car the stumble is barely noticeable. Gasoline?
I'm embarking on this quest too. '13 C2 7MT, 33k miles, I often feel hesitation between 2-3k rpms, such as when taking a turn at a traffic light in second and then accelerating with semi-aggressive throttle. It gets louder but feels weak, notably pulling timing. Runs great in the higher rpm range when driven hard. My car had new spark plugs last year/3k miles ago, but the coils were not replaced. OBD II scan shows no codes, but the "last/current drive misfire count" and "rolling misfire count last 10 drives" counts reveal single-digit counts per cylinder, above 0 but below 10 on each. I'm going to replace all the ignition coils along with the Variocam solenoids, see if there's any improvement, and then try a 93 octane tune.
Update: went to the dealer to have them do some service and warranty recall work. I let my advisor know about the stumble issue and he said he was "aware" of it and to see what I think after the PDK refresh and DME reset. The DME update and PDK reflash seems pretty darn good. I'm going to drive it for a couple more days to see if it comes back or stays away, but for right now its awesome. !st to 2nd is very pronounced sometimes when shifting in manual mode. But overall smoother shifts when driving normally and high engagement when mashing the gas pedal. Recall # AMCO Campaign scope 1
Ask your dealer about the DME, I did not do the gasoline emissions recall and he could not find that campaign with my VIN#. The PDK and DME were a combined campaign.
The other items in the recall:
Heat shielding recall # WLA4 corrosion protection, rivets on crossmember
Replacement tank leakage diagnosis module #WLC8 tank leak module / air filter / Pressure switch
Last edited by GermanCarFan1; 06-16-2023 at 08:46 PM.
Reason: more info
I'm embarking on this quest too. '13 C2 7MT, 33k miles, I often feel hesitation between 2-3k rpms, such as when taking a turn at a traffic light in second and then accelerating with semi-aggressive throttle. It gets louder but feels weak, notably pulling timing. Runs great in the higher rpm range when driven hard. My car had new spark plugs last year/3k miles ago, but the coils were not replaced. OBD II scan shows no codes, but the "last/current drive misfire count" and "rolling misfire count last 10 drives" counts reveal single-digit counts per cylinder, above 0 but below 10 on each. I'm going to replace all the ignition coils along with the Variocam solenoids, see if there's any improvement, and then try a 93 octane tune.
Ya mine shows the same misfire count..is this normal for non-stumble cars?
don’t bother with the coils. I did new plugs and coils also. No diff.
Originally Posted by duxsi
I remain convinced that it's in the DME.
Every time the dealer performed a s/w update or reset the DME, the car drove like a different car for 48 hrs and the power band was as smooth as silk.
After a day or two the stumble returned.
Oddly enough, ever since I moved to Europe with the car the stumble is barely noticeable. Gasoline?
I agree. the DME is learning something ..but from what?
Originally Posted by GermanCarFan1
Update: went to the dealer to have them do some service and warranty recall work. I let my advisor know about the stumble issue and he said he was "aware" of it and to see what I think after the PDK refresh and DME reset. The DME update and PDK reflash seems pretty darn good. I'm going to drive it for a couple more days to see if it comes back or stays away, but for right now its awesome. !st to 2nd is very pronounced sometimes when shifting in manual mode. But overall smoother shifts when driving normally and high engagement when mashing the gas pedal. Recall # AMCO Campaign scope 1
Ask your dealer about the DME, I did not do the gasoline emissions recall and he could not find that campaign with my VIN#. The PDK and DME were a combined campaign.
The other items in the recall:
Heat shielding recall # WLA4 corrosion protection, rivets on crossmember
Replacement tank leakage diagnosis module #WLC8 tank leak module / air filter / Pressure switch
Originally Posted by Jack F
I believe there is a PDK recalibration. Those with the hesitation, you have had this done?
PDK recalibration ..I did that when I changed the PDK clutch oil. Didn’t make a diff
I guess I will pay dealer the visit and see what I can find in terms of updates for DME.
my mechanic worked with tech from the nearby dealership and I thought he uploaded some DME updates.
Invoice says:
“ Perform adaptation for throttle body. Perform adaptation for PDK. Perform DME program and reset adaptations.“
“Check engine connections, upload DME program with Porsche system tester”
Ya mine shows the same misfire count..is this normal for non-stumble cars?
don’t bother with the coils. I did new plugs and coils also. No diff.
Eh, I've had coils bite me on two other ~10yr old european cars, and it's a '13, so I figure it's cheap maintenance at ~$240 DIY and then I don't have to worry about it. But yeah, maybe wishful thinking that it's the problem since it's buttery smooth at higher revs.
06-07-2023, 09:16 PM
