jmoorenc

My 04 cayenne turbo had the same issues with intermittent stumbling and it ended up being the left fuel pump. I spent one Saturday replacing both fuel pumps plus the regulator and the filter all at the same time. No issues since. My initial codes were for misfires as well. If you do this job yourself make sure you take notice of how all the hoses inside the tank are connected together and to the fuel pumps and regulator. It’s easy to hook them back up wrong like I did. Sent from my iPhone using Tapatalk

One thing I would add is if you remove the throttle body for cleaning you may want to remove the side cover and clean the TPS with contact cleaner. No matter how clean the throttle body is the car has to know at all times what position it is in. My fx35 had a dead spot in the throttle position sensor and often searched for the correct idle position at start up. Idles as smooth as silk since addressing that.

I recently (3 weeks ago) purchased a 955 Cayenne Turbo and had the same idle drop issue. After purchasing, I discovered the water pump was leaking which seemed like a good DIY project that would allow me to get familiar with the vehicle. The first water pump I purchased and installed was an aftermarket Laso and in less than a week it began making a groaning noise. During the replacement I pulled and cleaned the throttle body and after putting everything back together it made no difference with the idle drop even after performing the throttle position relearn sequence. Last week it was unusually cold here and when going over speed bumps the front of the vehicle was making a noticeable scrubbing/squeaking noise. I purchased some spray silicone approved for plastics and bushings then sprayed everything on the front end down. I decided to open the hood and empty the can on the engine for some added protection on the hoses. While spraying I discovered a couple of hose leaks. One was on the purge solenoid inlet hose that sits to the right of the throttle body and the other was on the small line that hooks in under the intake "T" pipe. The one under the intake surprised me because I thought I had pushed it up within an inch of its life but you really have to fully seat it onto the nipple so it doesn't leak. Fixing those two leaks made a huge difference and the idle drop was almost gone. Last Saturday morning I took everything back apart and installed another new water pump but this time used one from the Porsche dealership. While everything was torn down I replaced some of the older hose clamps and made extra sure every hose was on and secure with no leaks. When putting the "T" pipe back on I finally got the nipple lined up perfectly with the fitting and saw how much further it actually seats together. Before starting the vehicle I performed another throttle position relearn. Knock on wood I have driven over 300 miles since then with no idle drop issues! It's made a huge difference in the way the Cayenne performs. I couldn't be more thrilled. Oddly enough my starter was grinding after almost every start and it has not done it since. I'm assuming maybe the auto start feature was keeping the vehicle starter engaged because the engine was not starting with enough rpms for it to sense to disengage the starter. Whatever the case may be I no longer am having the idle drop. One more thing to note is there is a huge difference in how steady the temperature is after replacing the water pump with the Porsche part. With the original water pump that was worn out and the new Laso I had temperature fluctuates for the few weeks I was able to drive the car while they were installed. With the Porsche water pump I am at a steady 180 while driving and at idle. There is also a difference in the pitch of the impeller vanes between the Porsche and Laso. The Porsche impeller seems to have more pitch on the vanes. Maybe it moves more fluid? Not sure but, again, I am thrilled with how smooth the Cayenne is running as of this writing. The final 2 repairs I have to make are the tensioner pulley and the drive shaft. I will update about the idle to confirm if it remains smooth over time.