NF4710

Lately I've felt my idle might be rougher than normal (haven't been driving the car much so it might be in my head). Scanned my C2S using iCarsoft - no codes at all. I decided to look into the DME records and here's what I found: in the last 10 ignitions. Here's the data I found:

Admittedly I'm no expert and am not sure what to make of this - appears I've had a few misfires in the last 10 ignitions. Plugs were changed 6 months ago (1k miles ago) at the dealer. Fresh tank of Top Tier gas. Again no warning lights and car drives great (except the idle may be a little rougher than I remember or perhaps I've been driving my AMG too much and have gotten used to a smoother idle).

M100_Ignition counter misfire detection ----- 2000
M210_Misfire counter, cylinder 1 ----- 0
M220_Misfire counter cylinder 2 ----- 0
M230_Misfire counter cylinder 3 ----- 0
M240_Misfire counter, cylinder 4 ----- 0
M250_Misfire counter cylinder 5 ----- 0
M260_Misfire counter cylinder 6 ----- 0
M310_Misfire counter, 10 trips, cylinder 1 ----- 4
M320_Misfire counter, 10 trips, cylinder 2 ----- 3
M330_Misfire counter, 10 trips, cylinder 3 ----- 4
M340_Misfire counter, 10 trips, cylinder 4 ----- 7
M350_Misfire counter, 10 trips, cylinder 5 ----- 5
M360_Misfire counter, 10 trips, cylinder 6 ----- 4

Should I be concerned about these misfires? Car drives fine otherwise.

Thanks,
NF

Jack F

So the car drives fine. Idles maybe a bit rougher in park or at a strop light. Idles rougher after engine is up to operating temp?

NF4710

Yes, even at operating temp I notice the idle seems a little rougher than I can recall. It's very subtle though.

NF

Stealth 993

That a very low misfire count. A rough idle is usually a intake vacuum leak. But it can also be ignition, or fuel based. But the last 2 usually do not go away, and will show up in the RPM range as well as idle.

I would go out and drive it like you stole it for a bit (drive WOT to redline), get it nice and hot then see how it behaves. Good old "Italian Tune Up" works wonders.

BSO

When I first drove my C4S after delivery 2 years ago, I used Chevron 93 because the Techron additive had been praised by numerous car media types.

The engine would have an irregular idle (it’s a manual), not terrible, but there all the time. This persisted past the break in miles.

An episode of Engineering Explained brought up Shell premium gas as an effective gas in preventing carbon buildup and generally good for the injectors as well.

Within a few tankfuls of Shell 93, the car idled noticeably better. I’ve used for about a year now and the idle is steady with a slight skip every once in a great while. I won’t put in any other gas now, Shell is doing something right in my view.

If it’s available in your area try it, it may do the same for you. BTW, my car has 14k miles.

Stealth 993

On a similar note, my friend with a 996 GT3, had the same issue, and he put in pure gas without ethanol, that made the car much happier.

vanlieremead

I did this once. That cop was surprised.

NF4710

An update on this thread: Car has been driving well but the idle remains a little rougher than I remember. Repeated a DME interrogation today: MIsfire counters M310-360 demonstrates 4-7 misfires per cylinder (which appear to be distributed on both banks). The Ignition counter misfire detection gave me a value of 1924.

I'm not sure what these numbers mean but would love some advice as I need to have the car serviced in the next few months and am debating whether I change coil packs (just did plugs at the dealer less than 1500 miles and 1 year ago), have MAF cleaned, or replace the variocam solenoids (seems a bit early at 28k miles). Alternatively for all I know these values could be normal - the car has had no lights or warning.

Thanks,
NF

PTSFX

Agree with this. Once upon a time I had a C5 Corvette and the CEL would come on if I put anything other than Shell in it...

AdamSanta85

FWIW our cars don’t have MAF’s.


Maybe try some BG 44K injector cleaner or similar.

Jack F

I have always heard BG 44K was a very good product. Do you use it in your 911.

AdamSanta85

I haven’t used it in my 911 (yet). I do use it as factory recommended in my Land Rover LR4 direct injection engine every so often. They use it to clear up idle issues and slight misfires.

https://www.draytondistributors.com/...BG-208-44K.pdf

I have heard of Porsche dealerships using it.

It might help OP if his misfire is caused by slightly dirty injector nozzles

NF4710

Actually the dealer did a BG44 with my last oil change (9 months and 1500 miles ago). Not sure if repeating is good since I hear it can dilute the oil.

NF

Tier1Terrier

This thread has piqued my interest on a few things... First @NF4710 Am I understanding correctly that you were able to DME "interrogation" with the ICarSoft tool? Are you able to obtain similar data on over-revs like the dealer does with DME reports? Please pardon my lack of understanding of what a DME interrogation is vs. what people refer to as DME reports.

The other thing that I'm curious about in this thread is of people talking about fuel additives. I've been digging around trying to figure out if this is something I should do periodically to maintain good engine health. The more popular consensus I've encountered is it's not necessary if regularly fueling from big name gas stations like Shell, Chevron, Mobil, BP, etc. It's something I don't want to do if it could potentially have ill effects but definitely want to do if it can prolong engine life / performance. Just to add my 991.2 is just over 4 years old with <10k miles.

NF4710

I haven’t been able to pull DME reports. But in icarsoft there is a DME menu for the 991 and that is where this data has come from. Again the car has had no warning lights or faults.


NF