I'm in exactly the same boat here- also 2008 CTT, incredibly frustrating. Plugs & coils changed. Divertor valves changed. No obvious vac leaks or errors on Durametric (apart from a persistent P1248 (or maybe 1208?) I think it said low boost pressure, but I also think this is a persistent code from before the divertors were changed and that my Durametric cannot clear this code)

Car is at mechanic to diagnose, despite apparently being a Porsche specialist, he now tells me that he's 'checked all the sensors' and now he wants to temporarily swap in a known working N75 valve boost control valve to rule this out (which is crazy considering this is a ~35 dollar part).

All this has taken just over 2 weeks so far.

Any ideas peeps - perhaps the OP solved the problem and ne's still around? (long shot!!).

cheers guys.

Rich

 

Everything you have described is what I went through with my 4.5 CTT
I have now solved my issues and the car is strong and enjoyable to drive
What I found to be the issue.
Oil air separator diaphragm leak. $110
Build up of oil in the LHS lower intercooler pipe 1 hours labour.
Lastly, cleaned excess oil out of K&Ns. 20 minutes

good luck

 

Hey...I have EXACTLY the same problem!!! Also a 957 2008 CTT (build date late 2007).

I've checked some possible causes and have done the following (but no crankshaft position sensor problems that I'm aware of

• new upper and lower front control arms because the LBJ rubber was perished and I stupidly thought it would sort the vibration problem.
• I've had the wheels balanced at least 5 times + new tires all around.
• New spark plugs and coils (genuine Porsche from ECS)
• New divertor valves
• I've been told the throttle body and MAF sensors were cleaned, but I'm doubtful of the honestly of the place that claimed this.
• New valve cover gaskets and sparkplug seals (mainly because of a small oil leak)

Sometimes I get a pronounced stutter or shuddering on gentle (not heavy) acceleration above about 50km/h. It seems to me that the 'shudder' or 'stutter' is a separate issue from the 'vibration', and appears to 'come and go' - I've noticed that different brands/grades of fuel MAY have an effect on this??? - I actually took the car to a mechanic yesterday because of this problem, but also a more urgent fuel leak smell (possibly fuel filter flange), and also a 'rattling' noise like a worn pulley but coming from the rear of the driver side engine/scuttle area - it was his opinion that the noise was not engine related but something behind the scuttle, anyway I'll be taking it back in a few days when the fuel level is reduced (to access the fuel filter flange easier) so they can check out all these issues, but the guy was 'touching' a few things on top of the engine, and he gave the crankcase vent pipe a good nudge ( https://www.europaparts.com/crankcas...810724553.html ), and now the engine MAY be smoother ...From a bit of research it may be possible that this breather hose could contribute to stuttering acceleration etc...I'll have a closer look at this pipe later today to see if I can see anything obvious...

ANYWAY...After 16 months and only 10k KM of ownership (not driven much due to COVID) I've realised that the vibration, is ALSO present in NEUTRAL or PARK, at exactly (ish!) 1625RPM AND 2050 RPM. It's difficult to feather the gas pedal because it's quite sensitive, but when you do, you get exactly the same strong vibration sensation through the seat as you do at 80 - 110 ish KMH (55-65 MPH approx.)...

I believe the car has new engine mounts (related to blown coolant pipes, I believe that access to replace the engine mounts becomes available when the gearbox is removed to access the coolant pipes, or alternatively the entire subframe was removed - I’m not entirely sure, but I have the old invoice from the previous owner showing new engine mounts in 2017).

I explained all this to the mechanic yesterday, and to be honest he seemed very unsure about it all. My current suspicion is the harmonic balancer on the crankshaft, other than that I’m clueless! Like the OP, any help would be appreciated (I'd happily pay for accurate advice!!! - actually maybe I should bite the bullet and take it to the main dealer?? - I'm in Oman - not many knowledgeable mechanics here for German cars))

I hope the above might also help someone else. I'll try and keep this thread live and report what (if anything the mechanic finds when I take the car back)...Who knows perhaps the rattling, petrol smell and vibrations/stuttering are all related!!

ps. there's no CEL, and I haven’t scanned it lately, but I used to have a perpetual 'underboost' code, not solved by the new divertor valves (however I may have read that the codes for this can't be cleared by Durametric which is what I’m using).

Cheers

Rich

 

Ctt roughness.

I would be checking

Cam timing solenoids
Air oil separator
Boost control valve
vacuum leaks

Gibbsy

 

Quick update. I was 'WFH' this morning, so I had a quick look around the car.

I took off the Air Oil Separator 'lid' and found that the membrane was perished. When I folded it the other way for inspection, it split apart. Not sure if I was the final straw, or it was already broken but invisible until manipulated. I've since ordered:

Membrane for 94810513107 Porsche Cayenne 4,5L 450PS 1 $19.90

And

Diaphragm valve for crankcase ventilation Porsche Cayenne 4.8L M48.01, M48.51 1 $19.90

I ordered both since it was unclear which one is correct, and they're pretty cheap. I'm still a little confused, because I'm sure mine was different again when I was checking it out earler today (i.e. the hard retainer disc seemed to be integrated into the silicone disc...wheraes they are seperate parts on all other pictures I've seen...I should have taken photos...)

Also, I removed the rear bench seat and accessed the fuel tank hatches. Driver's side was fine. Passenger side is spraying fuel everywhere!! Currently zip tied it to stop fuel leakage and driving it around until the tank is near empty (to allow easier replacement).

I also found an uncapped t-piece at the rear of the engine on the passenger side with a strong vacuum felt when putting finger over it, and hissing loudly. I found some pics online showing it capped. I found a small screw and blocked it off. It doesn’t seem to have affected the drivability....

Regarding the rattling in the scuttle area, I discovered it was a metal retaining clip for the currently removed plastic vanity covers! (that noise had been mystifying me for months!!)

 

Temp repaired the diaphragm with cling film and it's fixed the problem it seems. Car feels lovely and smooth, really like i've never experienced!! However, the idle has become lumpy. I'm assuming the diaphragm leak 'profile' has now changed (didn't get a perfect seal with the cling film), hence slightly different symptoms.

Can't wait for the replacement diaphragm to get here!

However when I got home to remove the cling film (didn't want it disappearing into the engine), I found that the plastic cover of the camshaft adjuster, just below the AOS, pictured below (before the oil accident), had 'shot' off, and oil had been squirting (at some pressure) up into the underside of the bonnet! Now i'm a bit puzzled...

I was also wondering if this might be related to my blocking up the t-piece with a wood screw and bicycle inner tube dust cap...Perhaps someone could confirm (perhaps have a quick look at your car??) and tell me what this pipe is, and if it should be open to atmosphere, or blocked off....or connected to something else...kinda looks a little incongruous to me..

Oh, and this morning the starter didn't want to turn, and then 3 seconds later (when I assumed I had a flat battery,) it roared into life at the next key turn...suspecting dying starter...

one day I'm sure that (mostly) everything will be fixed!!!

 

Maybe this will help. My 04 CTT was a little sluggish off the line and liked to store extra oil at the bottom of the DS charge pipe as it enters the IC. Anyway, I replaced the torn diaphraghm and... better but not perfect... then I checked and changed the check valve pipes between the diaphraghm and the intake manifold. Problem solved.

The PCV relieves excess crankcase pressure caused by blow-by and recirculates this dirty mist back into the intake for burning. So far, so good. But remember, this is a Turbo, so our manifolds will not only see varying degrees of vaccum, but also Boost. That boost would blow right past the PCV and into the crankcase and - like a drunk penguin- would start blowing seals. Oil leaks everywhere. Fortunately we have these check valves. The elbow downstream ot the PCV in you last photo shows a check valve . This rubber diaphraghm check valve prevents turbo pressure in the intake from blowing backwards into the PCV and down into the crankcase. It is torn, and you are blowing boost into the PCV. An your engine might be leaky as a result.

 

@Richard Godsall - How was the result after you replaced the diaphragm? I have an '08 CTT with over 100k, and having the same symptoms... just got it, so just starting to try and diagnose. Any updates helpful!

Cheers,

D

 

I can't speak for the 957, but in my earlier 2004 955 CTT, replacing both the PCV Diaphragm and the check valve solved my stumble & oil consumption issues. I was previously adding a quart every 1,500 to 2,000 miles. Now, 5,000 miles and no oil consumption. Your check valve assembly is between the PCV and the intake and looks different from the earlier one - same function though - prevents boost in the intake manifold from overwhelming the PCV.