Corvetteboy6988

Ok, ive been fighting drivability problems for weeks now, 2005 CTT, 105,000 miles.
I have done and or checked all the usual, triple checked in most cases.
Within the past week, brand new berus, plugs, battery, valve cover gaskets, smoked multiple places multiple times with no leaks, compression test good, fuel pressure good, all vac lines are 2 years old or less. Orings are new on all charge pipes, etc.
I did have 1 CEL this past month during the poor running, the vacuum booster pump circuit. It kept blowing fuse #12, car would no longer adjust trims, stayed at 0 or all trims Replaced fuse and pump, no codes, thought I was good, was running noticably better. Started by driving it easy, seems normal, but then after a couple days im ready to drive ot normal, get on it with boost, it runs rough, surges, is low on power, and then after boosting it just idles rough. Back to the drivability issues. I do get full boost, no issues there, diverters are 3 years old. I can tell itc just doesnt sound right, feels like its missing a bit, and all the surging and lack of power under boost.

Here is the real question and discovery. When diagnosing the vac booster pump I discovered pumping the brakes is what caused the fuse to blow and pointed me to the pump, but I also heard a suction/vac leak sound from what seems like under the rear of the intake.
I thought the new vac pump would solve this but I still hear the noise and feel the engine stumble a bit and then idle bump up and smell rich exhaust. I decided to watch fuel trims when pumping the brakes, and they jump from around 0 to -2 normally idling up to 12-15 %, idle jumps up a bit, I hear the suction sound, smell the rich running exhaust. The vac pump does come on as it should for 5 seconds or so, its working but something else is off. At the same time I watched misfire/fault log counter, cyl 4 and 8 start showing additional misfires while pumping. All other cylinders are very low cumulative counts, 30s or so, 4 and 8 are in the 200-300s, whatever it is is affecting the back two cyls the most.

Is this normal, the positive jump in fuel trims, the suction sound in addition to the normal vac pump coming on? I really don't think so.
can someone try this?
why cyls 4 and 8, this all has to be related to my drivability issues?

Its seems like I have a vac leak inb the brake booster circuit, yet smoking has shown nothing. Maybe 1 way valves on brake booster system is not allowing me to smoke all the lines?
there aren't any vac lines under the intake that I am aware of to check.

Im gonna pull the cowl next, already did the line running to the brake booster and the grommet, but who knows.
Ill pull the intake after that to look for anything.
could the intake manifold have a crack? I did get an FVD tune this spring, from the higher boost?
All hoses at the back ofthe intake manifold look fine, and i smoked the one from the booster pump that 90s into the rear of they intake, no leaks. I smoked the whole intake from the throttle body also, no leaks.

Normal idle short term trims:


When pumping the brakes, rich trims, fault counts increase:

Ill try to get videos up to see the trims change real time, and to hear the suction sound and idle change.

Other thread with the previous saga of frustring troubleshooting:
https://rennlist.com/forums/cayenne-955-957-2003-2010/1424399-fault-uneven-running-misfire-counters-recent-issues-after-using-redline-0w40-5.html#post19624631

VoilaGT3

Had a similar problem in my 911. Replaced the booster and it stopped. I would notice an idle change when depressing the brake after start and if I kept pumping it would bog till stall.

Corvetteboy6988

VoilaGT3, any engine issues when this happened for you?
my brakes actually feel fine, it's the roughness, surging, lack of power under boost that's most obvious.

VoilaGT3

No, brakes were fine as well, till they werent lol. Surging under boost? Any issues in park at high idle? First things that come to mind are PCV or fuel.
From your other post it seems you have been going at this for a minute. My old school trick for finding vaccuum leaks is a can of carb cleaner. Clean idle, but unstable after means if the fuel and such are in order enough to run on default non-active wot, try cleaning your AFMs. Not sure how to check fuel pressures across rpm range, so beyond this point you are down to fuel pressure or engine management.
P.S. I am not greatly familiar with air pumps, but I know the 955's have them and I would have to wonder if the silenoid may be stuck open. My general thoughts are that would wreak havoc on sensors in the intake.

VoilaGT3

Or to nip it in the butt, send it to Karl @ RennsportKC.

Corvetteboy6988

Thanks for the tips I appreciate it.

Maybe a bad booster is what killed my vac pump, it was running too much and overheated, not to mention its old. The magnets inside were fairly rusty.

Forgot to mention, all the while this has been going on, ive had a smell I can't pin point underhood. Smells like oil, but im not leaking anything, im thinking is crank case fumes, which would align with some type of vac leak.
assuming the bad brake booster diaphragm is like a big vac leak, right?

I have cleaned the MAFs, and I have a newer MAP.

I can rev and hold the idle high, seems normal.
AOS diaphragm and hoses going to it are fine, smoke and inspected diaphragm, replace it last year.

Air pumps, you mean the air injection pumps? Aheady checked them, cause they are on the xsame circuit as the vac pump. They are realively new, 5 years old. I also checked the egr valves the run into, no leaking and they open when the pumps are on during a cold start.

VoilaGT3

Hmm, no leaks, smell of oil, particular happenstance of fail to start when warm and performance issues in boost. Have you checked oil consumption and turbo hoses? I would be surprised with no given codes, but excess oil burning off in the turbos and cooking the cats... just a thpught hopefully with all the Porsche guys in here this will spark some thought.