Hi all - I'm in Miami and I have a 2016 C2, unmodified, had her since October 2021. I bought her with 85k miles - we just broke 90k! I test drove a few before I bought her, a bit older (2012, 2013) but with less mileage but neither drove or sounded as good as the one I bought - she really does run wonderfully...most of the time. The idle had been a little jumpy since the beginning but only after the initial cold start idle burst and up until she's about 200 degrees (fluctuating from about 450-700 - and in sport mode after I've hit temperature she's rock steady at 800.) After 200 degrees and not in sport she's slightly wobbly - but sometimes she's solid at 650 - all so inconsistent. Also, when not fully warmed up I sense a little hesitation at times when accelerating hard-ish. There are no codes, and she doesn't stutter, no smoke and just a little soot in the tailpipe. The car had 1 owner who took immaculate care all with Porsche in Atlanta and all recorded. Since I got her, I've changed the oil and air filters, I then changed the plugs and coils - all work myself. Nothing has really affected the idle or hesitation much. I did notice the plugs indicate a slightly rich mixture. I got an iCarsoft OBD tool and checked all DME - only one code in its history - mass airflow implausibly high (strange given it doesn't have an MAF but an MAP?!) but no active codes, no CEL. Today I decided to learn more about an Air Oil Separator. I understand now how it works and what it does and how it routes so I decided to open the hose where it connects with the Plenum right after the TB and noticed some oil in the hose and inside the housing - not a lot but enough to coat my finger. My hypothesis is: the AOS is not functioning properly but it is working enough not to throw a code. It is leaking oil into my intake distributor and possibly fouling the Manifold Absolute Pressure sensor. The MAP is likely causing my rough idle, while the oil in the intake may be causing the richer mixture. I am an amateur who loves to learn and do but that's all - if anyone with real knowledge can please tell me if my assessment seems viable, plausible, way off, if I may be missing something? Can a bad AOS and fouled MAP cause the idle issues I described - and why wouldn't it affect the idle in sport mode?

As follow-up to this - I intend to change the AOS and MAP sensor myself but I'm wondering if it may also make sense to change the Crankcase Vent Valves on both banks as well? If anyone has a workshop manual for the CVV and AOS that would also be greatly appreciated. Again, Thank you for any input!

 

Here are a few different threads that are worth a read:

https://rennlist.com/forums/991/1267...esitation.html

https://rennlist.com/forums/991/9061...ble-issue.html

https://rennlist.com/forums/991/1154...le-idling.html

The consensus seems to be that replacing the AOS is a waste of time, but that's not to say it may not help in your specific case!

 

Thank you! These just opened up several holes for me to fall into - now I'll need to learn about the variocam solenoid!

 

On my new 911 three years ago, the idle was uneven. Was using Mobil premium. Found some information that indicated Shell premium is good at keeping internals cleaner.

Switched over to Shell, the idle became noticeably smoother and at a steady RPM. That’s the only gas I use now. Give it a try and run a burn a couple of tankfuls see if it works for you.

 

Thanks - I've been using Chevron 93 exclusively since I got her, I know Shell is good too but can't believe Chevron with Techron is causing this. I'll give Shell a try next fill-up and see what happens.

 

AOS is designed to have some oil-I don’t think this is the source of your problems. My money is on the vario cam sensors.

 

I just assumed these cars idle rough. Mine def idles pretty rough. I started feeling more idle vibration after changing out the OE muffler. I only use Shell gas.

 

Come to think of it…with 80k miles, you may have some direct injection deposits on the valves that are causing the issues. I know most don’t clean them in our cars like they do the newer BMWs and VWs (every 40k or so) using walnut blasting so it could be the issue. The only way to tell for sure is to pull the intake manifold…which is lots of work for sure. Maybe there is a way to get a endoscope in there?

 

The valves 100% could use a cleaning, but I don't think it's possible without the engine coming out.

There was a GT4 guy who gained 20whp back by cleaning his intake valves while the motor was out.

BG has an induction cleaning service that looks like it may help a bit, and it probably not terrible to do if you remove the rear wing.

 

Thank you - I thought the air return hose from AOS should be completely dry? Wouldn't oil in the air intake foul the MAP? Also, would it be the variocam sensor or the solenoid, or both? I'm looking at the factory service manual - cannot find any reference to the variocam sensors...anyone have a WM number or reference I can look at for variocam sensors?

 

Porsche DFI Injectors spray the back of the valves and it keeps them clean; they dont suffer the same issue other makers DFIs do.

 

Tear downs of 981 GT4 engines say otherwise.

It doesn’t appear as bad as some of the Audis and BMW’s but they still get gunked up.

 

Thank you all for chiming in. After much more research I've concluded it is more likely related to the VVT - symptoms seem to match. I noticed my MPG declined quite a bit when I added liquimoly fuel injector cleaner (the irony!) I'm now thinking it may have loosened some gunk and sullied the oil a bit. I ordered 2 new VVT solenoids as well as 2 VVT sensors (not touching the actuator just yet as that seems like a much bigger job.) I will report results after I change them and the oil. That said, for the life of me I cannot find any reference to the VVT sensor in the factory service manual - I scoured it and granted its about 8000 pages but there doesn't seem to be any mention of it whatsoever. I did see an image (but no reference or label) of the sensor in one of the pictures on the valve cover so I know where it is - does anyone have a WM on the vvt sensor? Could use the specs on torquing and any other important info that's not obvious. The WM for the VVT solenoid is WM 155519 if anyone needs it.

I now understand that a little oil coming from the AOS air return hose into the plenum is normal and since I don't really lose much oil (1 bar in 5k miles since last change) it's probably operating normally. The slight hesitation/stumble on acceleration and lowered MPG along with rough idle while car is cold seem to match the symptoms I've read. I don't think it could be full injectors or gunked-up valves as this problem would be pervasive, not only when the engine is cold. I believe the solenoid loosens up when the oil is hot which clears up blockages and then the engine runs fine. Also, after 3k RPM she runs solid even when cold. All symptoms of VVT from what I've read and seems to be a "known" - yet unacknowledged by Porsche issue - although if you look they're now on their fourth revision of the solenoid so perhaps tacitly acknowledging the issue. Again, appreciate the help and any other insights anyone cares to share.

 

GT4 guys are making custom catch can setups for their cars. We have same motor. Not a bad idea....

https://rennlist.com/forums/gt4-spyd...journal-6.html

Post 81 and back

 

I just got one of the AOS setups from @VektorPerformance . I should have it installed soon. Hopefully this will prevent the issues the OP is having?

Vector AOS

Edit to clarify, OP does have the turbo 3.0 right?