Porsche Cayenne S Rough Idle Stumble

Porsche Cayenne S Rough Idle Stumble

Does your Cayenne not feel smooth anymore? Porsche Cayenne S Rough Idle Stumble can be caused by a number of things, today we talk about ignition misfire diagnosis.

Modern engine electronic control units are more complex than ever. Not only do they have the task of running and managing the vehicles main source of propulsion, they also have to be able to identify problems that may be occurring with the motor. The ECU, or in this Porsche Cayenne S’s case, DME, has thousands of algorithms which run tests and checks that monitor the various running states of the vehicle. However, with as complicated as these computers are, they don’t catch everything, everytime. This Porsche Cayenne S Rough Idle Stumble is and example of one of those instances.

Porsche Cayenne S Rough Idle Stumble

This customer had a concern that the car was running rough and stumbling off idle. Doing a quick scan showed no faults, or anything that indicated an issue in the system.

When dealing with a no fault diagnostic condition, you need to go back to basics of an internal combustion engine, fuel, spark, compression and flow. The vehicle is obviously running well enough to be driven without setting a fault, so were looking for something that is still working, but not as well as it should. Testing the various components of this engine can be time consuming and expensive if the customer is paying for each step.

2006 Porsche Cayenne S 4.5 v8 Rough run idle not smooth stumble on acceleration ignition coil spark plugs no faults when cold or hot 0 autologic interior OBD 2 plug scan tool check

We first performed a smoke test of the intake system, but no leaks were present.

After watching the Cylinder smooth run deviation values, it was clear that bank 2 was running ever so slightly rougher than bank 1. Our vast experience with German vehicles has taught us that we need to see how this vehicle is actually running. The best way to do so is by removing the spark plugs and “reading” them. On the Cayenne, bank 1 cylinders have an additional amount that greatly increases the amount of time to access the spark plugs. In order to save the customer substantially, we decided to check only bank 2 spark plugs for now.

DS2006 Porsche Cayenne S 4.5 v8 Rough run idle not smooth stumble on acceleration ignition coil spark plugs no faults when cold or hot bank 2 coils beru

The condition of the spark plugs will tell us what to look for.

White plugs indicate a lean fuel mixture, heat, or contamination from a non-combustible substance.
Black plugs indicate a rich fuel mixture, or oil contamination.
Clean light brown colored plugs indicate a proper combustion event.
Extremely clean plugs indicate no spark or the cylinder being washed out by moisture vapor.

2006 Porsche Cayenne S 4.5 v8 Rough run idle not smooth stumble on acceleration ignition coil spark plugs no faults when cold or hot reading checking

There are other things to check for when reading plugs but for the sake of space these are the ones that pertain to this issue.

The plugs had a nice, very clean brownish look to them, meaning our misfire wasn’t a mixture issue. They looked pretty similar to each other so condemning one cylinder probably won’t fix this issue.

We have replaced ignition coils in the past for misfires, so it is in the realm of possibility that this particular bank of coils is just faulty enough to not trip the fault code. So while the plugs were out we swapped in good coils for the sake of testing, and the misfire, stumble, rough run issue was no longer present.

Just because there is no check engine light on the dash doesn’t mean that there isn’t something wrong with your vehicle. Luckily for this Cayenne S, ignition coils was all it took to get this vehicle running smooth again. If your vehicle is experiencing a rough idle, stumbling on acceleration or just doesn’t feel like it should, don’t hesitate to reach us by dialing 815-230-2900, or contact us through email at blog@fluidmotorunion.com. We’re conveniently located in the Naperville/Plainfield area of the Chicago Metropolitan suburbs.

  • Emmanuel
    Posted at 01:55h, 09 May

    My 2006 Porsche Cayenne s is not driving smoothly. When I slow down, there is delay in taking off. The car seem to be heavy, with loud cracking noise coming from the front drive wheel. This cracking noise is just for few second while try to take off after slowing down (say behind another car).
    The ride also seem to be rough and stumbling. You don,t feel that smoothness.
    The drive is better when on top speed, like on a highway.

  • fluidmotorunion
    Posted at 10:26h, 09 May

    I would suggest that this issue is not engine related but driveline related. Please have your driveline mounts, axles and driveshafts checked.

  • Lester Marfil
    Posted at 01:51h, 31 August

    Hi..I need your professional input on the issue of my 2014 Porsche Cayenne , the engine always idles rough on start in the morning worse when weather is cold but runs seem normally when engine gets warmed up already. Took it to dealer, they said they can’t find any fault on their diagnostics. I saw one suggestion in your blog, to change the coil packs and it solved the issue. I wonder if this same approach would help my car rough idling issue. Please let me know if it’s worth a solution and worth money spending on new set of coil packs.
    Thank you so much, I would really appreciate your input on this. Thank you so much.


  • fluidmotorunion
    Posted at 09:46h, 06 November

    That vehicle is direct injection. I would have a qualified shop check the fuel system first before I replaced coil packs. Injectors and high-pressure fuel pumps are known to cause those kinds of issues.

  • Ilyas Mohammed
    Posted at 08:14h, 22 July


    I could do with some advice. Porsche Cayenne 2004 4.5 S petrol had engine rebuilt 15 months ago pistons/valves /gaskets all replaced. Last week the vehicle started to feel groggy and done oil service and changed all spark plugs. One of the plugs had oil traces on it. The garage that rebuilt engine had only covered the work guarantee for 1 year. Just wanted to work out is it Valve cover gasket, head gasket Piston or engine valave issue. At point of if its a major piston issue then to scrap the vehicle not worth spending Thousands again for older vehicle. any advice appreciated.

  • fluidmotorunion
    Posted at 10:45h, 22 July

    Very difficult to determine the cause of the oil without seeing the car ourselves. What is the leak down percentage on that cylinder?

  • Dorian Castaignede
    Posted at 15:03h, 22 January

    Bonsoir combien vous vender votre moteur compler et combien de klm merci

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