I'm hoping a member can help me to understand what may be causing an engine stumble and hesitation affecting my '22 base Cayenne.

In a nutshell, my '22 base stumbles and hesitates when the engine is cold. This happens whenever the car is first started during summer or winter, and whether the car is in normal or sport mode. After the car's been driven a few miles and the engine has come up to temperature, the hesitations and stumbles cease and the car drives acceptably.

I am aware of member complaints about the base engine's rough idle, and my car is no exception to that problem. But the hesitation and stumbling first became apparent only within the past 10k or so miles (the car now has about 32k miles). I was hoping changing the plugs during the car's 30k mi maintenance would resolve the issue. But the car recently had that service (with no error codes reported), and the stumbling and hesitation continue unabated.

Does anyone have any ideas about what may be the cause? Or, in dealer-speak, is the hesitation/stumbling "normal" and "as designed"?

 

Try some injection cleaner in the fuel tank. These cars are sensitive to fuel deposits in the fuel injection. Always buy top tier fuel, too. Most engines do have some roughness to them until warmed up - how much is too much? A video would help

 

Spark, fuel, air.

You just had the plugs changed, correct?

Electrically, this leaves coils and sensors. Unlikely, but not impossible, that coils are degrading. Unlikely, but not impossible, that Variocam sensors or O2 sensors are degrading. Temp and intake pressure sensors are involved, and equally unlikely to be on their way out on a 2 year old car. In general, engine parts these days are produced to be cheaper than dirt for the car company. Bear in mind that Porsches are Volkswagens at the core.

Of the electrical bits, the Variocam sensors are the cheapest to replace. Then the temp and pressure/boost sensors, then the coils.

Fuel means tank lift pump, tank filter, high pressure pump and injectors. Everything is expensive and time consuming to replace in this chain. No systemic reports of fuel system failures for EA839 on rennlist or audiworld.

If you don't have CEL or codes and you don't smell fuel leaking, the dealer will likely be of no use to you. Either live with it or start throwing parts at it.

 

However, I think a visit to the dealer will be necessary. Unless you find an indy with the right software, knowledge and experience with Cayenne.
Blindly replacing the parts can be expensive and ineffective.
You need to connect a computer with the original PIWIS and measure various engine parameters (data flowing into the ECU) while driving and then compare them with the standard ones. These are many parameters that can be read and their deviations during engine operation under load should answer your questions.

 

Well this is interesting because I also have a “22 base with a stumbling problem. In my case, when the engine is cold after sitting overnight, if I drive away slowly it seriously balks at the 1-2 shift and throws you forward in the seat. I have 37,000 kms. on it and it has done it since shortly after I got it at 2,000 kms. It does it most of the time but not always and I can’t figure out a pattern. For the most part it is only on the first 1-2 shift and other than that it is smooth and there is no stumbling or hesitation. I seem to get around the problem by putting it in manual 1st gear to start off then shift to auto. I have mentioned it to the dealer but have never taken it in for a reflash or diagnosis as I never seem to have the time.

 

@LSR What brand and grade of fuel do you use most often?

 

In my case, always Top Tier and mostly Shell 91.

 

I always use Shell, Mobil, or Sunoco 93 octane.

What would happen to the engine if lower octane is used? Would that damage the engine, and if so how?

 

Unknowable. The manufacturer recommends premium and you state you are adhering to this.

 

Your Cayenne will do just fine on 91 (RON + MON) / 2, also known as 91 AKI (Anti Knock Index). Porsche specifies 90 AKI as an approved alternate fuel. They also specify a maximum of 15% ethanol blended into the fuel.

In an emergency, Porsche says you can burn 86-89 AKI but you should not use full throttle. Never burn lower than 86 AKI.

I suspect that most Cayennes in Western U.S. are burning 91 octane, as this map of 93 octane stations demonstrates.

Complete thread on fuel requirements here:
https://rennlist.com/forums/cayenne-...for-stock.html

 

It’s not the Octane, it’s the Detergents in the fuel, that’s what “Top Tier” means. Cheap fuel has less detergents = more chance of injector clogging.

run a bottle of injector cleaner through your gas tank periodically.

 

I haven't tried injector cleaner. If that works, will it work with the first tankful? Or will I need to use it multiple times before I see improvement?

I ran a bottle of dry gas through the system a few months back, thinking there might be excess water in the tank (a problem back in the 80s and 90s) but that didn't work.

 

Maybe, maybe not. But its certainly not going to hurt anything. I run a bottle through each of my fuel injected vehicles quarterly. It's not to remove water, its to clean the injectors.

Porsche makes it own brand if you want factory approved, I buy this. YMMV,

 

I've had good success with Techron Concentrate Plus.

Allow the fuel level in your tank get to about 1/2 and then add a full bottle of Techron (20 ounces). Run the heck out of your car making sure that the engine gets to full operating temperature. (The photo below of the product shows a 12 ounce bottle, but you need to get the 20 ounce size. The link below is for the 20 ounce size.)

Then fill the tank with fuel.

The concentrated level of Techron that you run initially through your system should help provide more effective fuel system cleaning.

 

What does the dealer say about the problem? It's under warranty, right?