3.4 engine here. 7MT. I've had an ongoing frustration with a lack of smooth running at certain RPMs, and a lack of smooth acceleration on light throttle through an RPM range. This is probably not related to the variable cam adjustment that happens around 3K RPM that has been discussed elsewhere.

It almost feels like water in the fuel - that kind of subtle hesitation and stumbling. I have tried many types of gasoline to rule out particular gas formulations. I always use 93 octane. This has been going on for many, many months, but I think it's getting worse.

I've taken it to the dealer twice now about this and each time they say no codes, so therefore it's "fine" and "normal". But this past weekend I reached the point where I wasn't even having fun driving my car. I was filled with worry about what's wrong, and just wanted to get home to get out. That's not good for anybody.

So, my questions:

1) Should I go to an independent shop and get a second opinion? I just wonder if the independents have seen enough 991s to know, but I have no idea.

2) Does anyone have any tips on trying to rule things out myself?

3) Am I expecting too much? Should I not expect a smooth engine feel when cruising or accelerating? If that's the case, then I can adjust my mental picture. I just need to know if I'm out of line here.

Thanks! I appreciate the helpful responses.

 

how many miles?

 

Tell me about your driving style. Where are you typically shifting (RPM)? Have you tried any fuel system cleaners like Chevron's with Techron?

 

FWIW, my 3.4L 7MT with 31K miles has never missed a beat. Not sure exactly what you're describing, but I'm sure mine doesn't do it. I'm very impressed with how smoothly it pulls at any rpm, whether lugging it around at 2K, or redlining it.

 

6100

 

I'm not an aggressive driver nor do I tend to let it get up too high in RPM. I know, I know, I need to try doing that. Occasionally I will put it in Sport mode once oil is at temp and let it get up to 5000 or 6000 RPM now that I'm well past break-in. But if I'm doing 25 mph in my quiet neighborhood I'm going to be at 2300 RPM in 2nd gear - that's just reality. I'll generally shift at 3500-ish. I ignore the shift indicator because if I followed its advice I would definitely be lugging the engine.

I have not tried any fuel system cleaners.

Thanks in advance for your assistance. It's frustrating that it seems like the dealer is just telling me that I'm crazy. Hmmm... Maybe they're on to something. But seriously, just trying to pin point possible causes so I can chart my next steps.

 

Had same issue and cured it with a pint of Techron (available at Walmart of all places). Car showed no codes according to dealer.

 

Stealth, if you decide to try the Techron, I'd suggest 2 full tank treatments, then fill with untreated fuel, and get an oil change.

 

IMO,your car is way too new and has just few K miles to think the fuel system needs cleaning. If you're using the best octane gas from top tier brands you should be good.
Regarding your trip to the dealer : I'm sure their PIWIS tool will show them any codes,even pending ones...but I do wonder if they take their time to look at some live data from the car's DME. I would drive it around with the tool hooked up and look at the misfire counters on each cylinders at different RPMs. If it's registering just a few misfire counters on one of the cylinders and only at a certain RPM,they might not get picked up by the DME to set a code and could take longer to manifest. It could be a malfunctioning coil on its way out. I would also take a look at the fuel trims to see what they're doing. Again,all this needs time and it's related to your particular dealer's service department technician patience and willingness to do that for you.

Good luck!

 

Put it on a variable load dyno and get a graph of what it is doing.
You need that as proof of the issue.
Then you have a chance of getting it acknowledged and fixed from there.

I had a PDK Boxter S loaner (3.4).
It was smooth and no signs of what you describe.

My thought is your car may have a changeover valve issue on one of the COV that control the intake or engine vacum system.
Those COV dont seem to set codes when they fail.

Exhaust valve wierdness might feel lile a stumble too since there would be a noticable effect on power at mid RPM.

 

Q: What is "too high in RPM"?
A: Beyond redline.

You cannot go "too high in RPM" in a 991. See: rev limiter.

I can only imagine how dreadfully babied your poor car was during "break-in".

I had a friend back in high school, worked at a Porsche shop, loved to tell me how all these 911's would come in "needing a tune". He would run them up and down the street a few times at redline and hand the now smoothly running car back to the owner. With a nice fat tune up charge, of course.

Yeah, yeah, DFI vs carbs, yadda, yadda. Fact is these things run so incredibly near perfect now that the least little departure from perfection stands out all the more. So you got a car that for the totality of its short 6000 mile life has been driven in a manner guaranteed to optimize the accumulation of carbon. And lo, its showing the first little signs of maybe having a little crap build up on the plugs. Shocking!

Take the car out, drive it as much as possible at "too high RPM". Worst that can happen, you scare yourself to death. Er, I mean generate some decisive engine codes.

 

I understand your general points and it may be the case indeed,but I wouldn't completely rule out a proper diagnostic.
Regarding your high school buddy,I do not know him personally,nor do I know your current relationship with him,but he is the exact definition of a dishonest technician and gives a bad name to the good and honest ones. Sorry,but to me that is not something to laugh about...

 

Wow...

 

My Panamera had break squeal issues when I purchased at 10,000 miles. The dealer said to take out and slam on the breaks. I did - - then after they replaced the breaks 'cause that did no good' I was fine.

With that said - an engine like these needs to be driven. Try it to see if it helps, plus the additive. It won't hurt and may be quicker than the dealer.

 

I followed factory recommendations. Statements like these do not help me. But I knew you'd be the one to chime in with something like this! Thanks.