I'm thinking of all the possible items to investigate. If anyone wants to help compile a list, please add on. I'd like to have a list of sensors and items that are relatively easy to replace to rule out potential faults.

- Throttle position sensor
- Throttle body
- O2 sensors
- High-pressure fuel pump
- Spark plugs
- Fuel filter
- Ignition coils

I'm sure there are all sorts of other sensors... Those who know more please chime in! I'm looking for things that would lead to the appropriate delivery of fuel / spark / air. So that's either a sensor feeding data into the ECU or the delivery mechanism itself. I know there are typical things (spark plugs) but what I need help with are the 991-specific things.

As I start down this path I would like to try to be methodical about it.

 

Have you considered speaking to the folks at GIAC Tuning that have an ECU flash for the both the 3.4 and 3.8 configurations. I understand that the flash is totally reversible. They may be willing to let you try their flash to see if they inadvertently solved this problem. It appears that their engineers have a pretty good handle on the ECU, its control of fuel/air mixture and all the sensors.

If I was in this situation, I would try anything. Just a thought.

 

I guess Porsche does not want to admit the problem but yet fixed for the 2016 "On models equipped with the PDK transmission, the mode switch has a "Sport Response" button, which pre-conditions the drivetrain for maximum acceleration."

 

Sadly this is not the issue as the stumble does not discriminate between PDK and MT.

 

Was not aware the issue was also in the MT.

 

I have a 7MT. It's very much an issue.

 

Just to gauge the severity of this problem... how often do you guys experience the stumble? Everyday? Once a week? Once a month?

I've experienced it very infrequently but when it happens it's usually in the worst situation like crossing a busy road.

 

For me it's very noticeable 75% of the time in 2nd or 3rd gear transiting 2600 rpm. I'd kill to only have it occur once a month.

 

Occurs 90% of the time and will consider trading left nut.

 

Every time I drive the car.

 

Every day for me, but must noticeable on the first drive in the morning at around 2000 RPM's.

 

This sounds grim. I would echo whoever suggested the re-flash. Might just solve the problem. Have't read this thread fully but wonder if Porsche have sorted out the problem on the later 991s. Imagine the only thing they'd have changed would have been software...

 

Interesting point as far as build dates. Anyone with a '14 or later experiencing the problem?

 

Mine's a '15 GTS. 5,500 miles and no engine issues so far.

Anyone else?

 

Yes, a couple of '14 owners also developed the problem.
See link to survey results.

https://www.6speedonline.com/forums/...y-results.html