koala

It's so hard to say what might be happening. The new solenoids are revision 03, the original ones in my 2013 MY (2012 production date) car are an 02 revision.

They definitely didn't look amazing, but at the end of the day there is oil circulating through there, so I think that is probably to be expected.

The stumble was present for me regardless of ambient temp, or engine temp for that matter.

koala

Well, that didn't take long. My stumble has been back again for the past couple of months. There are times when the car runs absolutely smoothly, and then other times when it feels like it is bucking back and forth as if you're coming off the clutch improperly.

It was really jerky and terrible early this morning, and then on my drive back home later in the morning, it ran 100% perfectly.

pfan

Collectively, over time, stumble sufferers have replaced almost every conceivable engine component to no avail. The fact that the problem usually reoccurs in short order seems indicative of the DME/ECU quickly re-learning its bad behaviors.

At the risk of sounding like a conspiracy theorist, what are the chances that this is possibly caused by or related to the current Porsche emissions "scandal." Porsche has allegedly altered hardware and software involved with emissions testing, and one can only wonder if a bug is hidden deep within the ECU.

One thing is sure .......... We're unlikely to ever know.

Porsche_nuts

Interesting thought. I think you may have hit on something.

koala

I'd gladly have the emissions software update applied if it solved this issue! I thought it was only for PDK cars, though.

I could also reset my ECU just to see if that does anything.

pfan

As I recall, many of us have seen the problem disappear for a short period by disconnecting the battery overnight.

sampelligrino

Anyone here had or have the experience of a stumble when lifting *off* of throttle between 3500-4k RPM on semi aggressive driving?

Maybe in 2nd gear, and/or 3rd? Below that RPM range, or above it no stumble at all..

koala

A quick data point here and a link to another thread, which prompted me to try one more part swap.

https://rennlist.com/forums/991/1207...itation-3.html

I happened upon a 2016 GT4 throttle pedal (same part number as the 991.1 throttle pedal). It was only $99 shipped, so I figured I didn't have a lot to lose. (Part number, btw, is 970.423.019.01)

I received the 2016 GT4 throttle pedal a few days ago. My cul-de-sac is still half snow/ice, but I decided to get the car out yesterday regardless. I knew there was a reason I got these crappy all-season tires

I drove it yesterday with the original throttle. Definitely, some stumble/hesitation as I typically find on most drives. I then parked back in the garage and swapped the throttle pedals out (easy job, other than I am extremely good at breaking clips, which I ended up doing with the sensor clip). I did the throttle reset procedure as I figured that might be a good step.

Today, I drove the car for about an hour. I could not reproduce the stumble in any way, shape or form no matter what I tried.

Only time will tell of course, but that was one of the most enjoyable drives I've ever had in the nearly 6 years that I've owned my 911.

pfan

Sounds very promising! Assuming this is in fact the fix, it's surprising that it turns out to be a relatively benign solution. I had assumed the problem was so deeply embedded in the ECU that it was hopeless. I've got the part on order, and am hoping the new part doesn't come with the current malfunction.

BTW, any tips for avoiding the sensor clip damage? Thanks.

koala

Only time will tell - I have no idea if this is the fix as I've had perfect driveability on many occasions over the years.

My best advice on not breaking the sensor clip is to just not be me - I am extremely skilled at breaking these things. Just take your time and try to wiggle it free with a small flathead screwdriver. I made the mistake of trying to hold it with a pair of needle nose pliers and I squeezed a bit too hard.

bokh

can i ask what is the procedure to reset the throttle on a 991.1?

koala

Put the key in the ignition and turn it to "on" (without starting the engine). Wait about 30-45 seconds and you'll hear the throttle plate make some noise. That's it!

Also, I've now done about 800-900 km since swapping the throttle pedal and I'm happy to say that the car has been driving great. I've still felt the stumble a couple of times, but it was far less noticeable. I'm merely used to how it feels so even a slight hesitation in that range gets my attention.

Sajan

Bumped to hear there’s no cure for this still!

What all did you try @koala?

koala

As far as I am concerned, the replacement throttle pedal *is* the cure.

edit - I've also tried:

• replacing the variocam solenoids
• throttle body replacement
• throttle reset countless times (nearly every drive)
• different fuels and fuel grades

It's been a lot of trial and error over the years. I could easily be forgetting other attempts to fix this

pfan

I also recently replaced the pedal assembly/potentiometer, and the results mirror yours. For the first few drives, the stumble was non-existent. Over the last couple of weeks, I will occasionally feel a very minor bump, but significantly lessened over the original, unmistakable, stumble.

P.S. - I'd like to see a Porsche tech remove the sensor clip without breaking it. Mine did not survive the process.