No rough idle at cold starts but for the first few feet of driving, the car tends to stutter. This only occurs if the car has been cold soaked below, say, 50 degrees overnight and I'm just using light throttle. There was a high pressure fuel pump replacement campaign that Porsche performed voluntarily on certain VIN's that I thought would help this but it didn't. Otherwise, the car starts up and goes on its way perfectly.

I'm sure you're right regarding an insidious loss of power. I've never dyno'd the car to know for sure but all outward signs are showing a healthy car. I'm very interested in this topic, as well. Can't wait to see the inside of one of these engines.

 

I was primarily a lurker on Audiworld and still get most of my news from Quattroworld Off-Topic forum. I'm not an active poster, but an avid reader of the forums.

Thanks for bringing this topic up - I had been wondering if this was going to be an issue (not that it prevented me from placing an order. )

 

It is definitely a US gas issue. You'll see considerable deposits with 87 (don't use it) octane versus 91/93 octane. Lexus also has the same issue.

You can spike once in a while:
https://www.6speedonline.com/forums/...on-2-93-a.html

Also could 991 owners confirm if 91 octane is recommended, unlike on 997s?

 

The recommendation for octane rating for the 991 is 93 (US), like the 997GT2.

 

US gas may be a factor, but, at least with the RS4, owners in Europe were having the same problems at similar mileage intevals.

 

If this is an issue it will start showing up as people put more miles on their cars. Its a wait and see.

 

Woah, your experience sounds very similar to my 09 S cab. In fact, the HPFP on my car was replaced 3 times. After a cold start, the first 50 feet or so the engine stutters on acceleration, but clears up after slight warmup.

 

brianja,
I understand your concerns and would like to offer my services. Let me borrow your new 991 for a day a month and I will make sure to blow out any carbon buildup. Because I am a nice guy, I will do it for free. This is just the king of guy that I am.

 

I guess what I would like to know is how you get carbon buildup on an intake valve? It should be closed when combustion takes place. With DFI it only opens to let air in. ???
Someone please explain if you know. If it is on the bottom of the valve just run the **** out of your car like I do!

 

haha. I can take care of that part myself, thank you very much. I'm used to a nice puff of smoke from my RS4 at WOT.

There is typically some overlap when both the exhaust and intake vales are open simultaneously. That's when some of the exhaust can wind up back above the valves and settle carbon on the backs of the intake valves. Then the heat of the engine bakes it on.

What about the 1st rule? Sheesh. I'm on OT too.

I'm glad to bring up the subject for discussion. It's nice to see a civilized discussion of it on here.

 

I had never considered DI being a bad thing... I can't imagine (although this is an assumption) that Porsche would overlook something like this.

 

Can't compare a VW/Audi engine to a Porsche...... I have 34k on my DI 997.2 and there is no carbon inside on outside of the car.... I do have 4 dirty exhuast tips...

 

Why yes you can....Porsche/Audi/VW whats the diff jk

There is NO documented info on P engines....because the 9A1 engine is DFI then it is THEORETICALLY at risk.

How do you know you have no crud on your valves? Have you unroofed and taken a peek? Pics?

I will be replacing my valves with an X51 kit (in shop now), I will extensively photograph my valves...this on a 2010 C2S with 26K miles.

 

Please post what you find! Thanks in advance!