rpilot

To the OP.. I do not know what the exact problem is, but DI engines are notorious for carbon buildup on intake valves. I really do not know how effective fuel system cleaners are in reality so I won't comment on them. What I will say is that I recommend funfzig's recommendation to rev the engine on a freeway for a while. It gives these deposits a chance to burn off if you have being spending a lot of time in low rpms. I am not sure how many miles you have on this car either, so this might not be the right advice, but it's worth a try.

If that does not help, insist there is problem to the dealer , stand firm and get it fixed. Try another dealer if that is an option. Have the dealer tech take a test drive. Complain to PCNA. Get it fixed, code or no code. I have dealt with many a dealer in my lifetime and this is not unique to Porsche dealers. Insist and re-insist there is a problem.

I personally would never recommend a third party shop, no matter how good to diagnose and fix a problem on an in-warranty new generation car. The problem could be anything... a defective spark plug. It may be the transmission. Either way trusting a third party shop is a very bad idea, IMO.

Good luck and keep us posted.

Jay-S

I agree with this. Also, I almost always get surveys on whether the dealership fixed my service issue. I said no once and it stirred things up. I was told the PCNA gives the dealers a lot of flak for any answer like that. Just sayin'...

drmatara

I had a similar issue with my 997 C2S...and after numerous visits to the dealer they finally figured out that one of the ignition coils was bad...changed it and all was beautiful again

wanderfalke

Your car should run smooth with a surge at higher rpms, but it should not stumble any time unless you lug the motor. I would put the service tech in the passenger seat and demonstrate the stumble.My car runs good at all speeds and so should yours. You should not have to pay out of pocket to have a indie find the problem. Good luck and godspeed getting the joy back.

wanderfalke

Did it throw a code ?

drmatara

apparently not since I had to go to the dealer many times...

stealthboy

Thanks for the advice; I think I will wait a few weeks and go back in - this time insisting someone rides with me. Just this morning driving in to work I was amazed - thinking "How in the world could the tech have driven this and consider it normal?" He apparently drove it for 6 miles. Are they incentivized to not find faults? I'm just baffled. He at least should have felt the hiccup at 3K RPM when accelerating through there. BTW - whoever mentioned the "fish nibbling on a line" feeling you have hit it exactly. That is the feeling when maintaining a constant speed.

On a slightly positive note, when I got it back from the dealer my service rep at least mentioned to let him know if it got worse - so they're not completely discounting my tale.

I'm trying not to escalate this up through manager levels at the dealer yet. I will give them one more try. I do have some connection with the general manager since I wrote a piece for my local PCA chapter magazine about my delivery experience and put them in a very favorable light. He was very appreciative, so I'm sure he would want to know if I'm unhappy.

chuck911

Wait a few weeks....
Just curious, have you tried wide open throttle to redline a few times?
Or still sticking to 2300-3500 all the time?

Tapeworm

I have a c4s and had bad 'stumbles' between 2500 and 3000 rpm while the car was under 2000 miles on light throttle. This was really annoying and made the car not fun to drive as I found myself driving around the issue, or having brief moments of 'what is wrong with this engine' constantly. I had the car in for servicing and insisted they do all updates, after this, the problem has been a lot better and now I have over 3000 miles, I hardly notice it at all. Even going into 2nd or 3rd gear and deliberately trying to use light throttle around 2800ish rpm doesn't result in the sort of stumbles I previously felt. I have not changed gas or my driving habits.

Maybe it was an issue at lower temperatures in Nov/Dec last year, or maybe ther are fuel additives that the Porsche doesn't like being used in the winter. I guess I will find out this winter if the problem returns.

The service update did not fix the issue immediately, but it has become less over time since then. Maybe the engine after an update is better at adapting to the fuel available here since then?

The problem was severe and I'm pretty disappointed at the lack of smoothness of the engine when I first had the car. The stumbles and the big steps in power delivery were not just my driving style or imagination - we have a number of cars and I have owned a number of Porsches in the past - none have 'rough engines' that 'stumble' during reving.

At 3000+ miles, like I said, almost all the symptoms are gone now and the car is very smooth throughout the rev range, so I'm happy. It really feels as if the engine is 'loosening' up as I put more miles on it. I just wish it had been like this from day one.

I would take the car to the dealer and be very specific, insist on them coming in a test drive, make sure the feel the problem. If they don't fix it, return it again until they do, or lemon law it. I would not take it to an independent - Porsche must know about this issue and I expect it takes an ECU and maybe sensor updates to fix. Maybe they have batches of O2 sensors that the ECU has a hard time adapting too or something?

stealthboy

Yes, absolutely I have been playing with WOT up to 7K RPM in a few occasions. It's been fun. I'm also intentionally driving in a higher RPM range for just normal "cruising" as well.

wanderfalke

Does your car burn oil? If it does not it would counter indicate improper break in.

chuck911

Okay, so have you noticed any improvement since doing this? The reason I ask is this was just a likely cause not a "sure thing" by any means. Lots of guys have experienced similar roughness that turned out to be caused by one or more failing ignition coils. If you had described normal use that would have been a prime candidate. But you said you drive 2300 to 3500 pretty much all the time, seldom use full throttle and hardly ever run it up even as "high" as 5000. Six thousand miles of that back when these things had carburetors, you'd be lucky to have it still start in the morning. Nowadays though the engines are sophisticated enough to deal with this sort of chronic off the band use. Not only fuel delivery but thermal management, variable valve lift and timing, these things all expand the viable range of use. Still, 2300 to 3500 when done almost exclusively is more in line with a farm tractor than a Porsche. (Not mutually exclusive, I know.)

Anyway, as sweet as being proven right will be it'll be all the better knowing you finally got your car running as it should.

Oh and by the way you will probably need to do more than "play" with WOT "on a few occasions". The 991 is so powerful it makes it really hard to significantly load the engine without going crazy illegal. Once or twice in 1st or 2nd is really nothing to the engine. Full throttle to redline in 4th is what you need, but that'll risk jail time. So what you want is a nice big steep hill where you can get the load without risking 140+. If you live anywhere near Stelvio, that would be great.

The other thing you can do of course is put the car on a dyno. Someone else suggested that, although the lack of mockery makes me wonder how many people really understand what that entails. They strap the car down like you can't believe and run it full throttle, with your car 5th or 6th, all the way to redline. Usually around 6000 RPM the car lets go a truly unbelievable blast of smoke as all sorts of accumulated crap is blown out. Same thing happens on the road, except that think about the loads, you're doing 150+, the blast dissipates fast and your attention is elsewhere anyway. Where was I? Oh yeah, that's what happens at 6000. They continue the dyno run all the way to redline. This last part takes a while, because unlike when you run it up in the lower gears this is done in top gear under maximum load. Have you ever stood by a 991 running flat out under full load at redline? Porsche builds them to do this for a full tank of gas.

So, anyway, how's it running now?

jlanka

LOL. Drove that pass 2 summers ago in a BMW 520D wagon. Killer pass but average car unfortunately.

chuck911

Yeah, and anyway there's some pretty famous climbs right here in the states. Point is, there just absolutely is no reason for being afraid of driving your 911. Its what they are MADE FOR!

stealthboy

No improvement at all yet - and it may just be because I'm more sensitive to it - but I think things have gotten slightly worse. The weather hasn't been cooperating too much here in the mid-atlantic lately, so this weekend I'm planning on a nice long spirited drive.