Most of the people with this issue have had it from day one more or less?

 

I found the following info that could shed some light on the engine stumble/hesitation problem. Click on the part description to go to the website (no affiliation). Scroll down to Failure Symptoms:

Lambda Oxygen Sensor. Porsche 997 MK2 3.6L/3.8L

Code: 9A160616802
Lambda Oxygen Sensor.
PORSCHE

Fits:
Porsche 997 MK2 3.6L (BEFORE Catalytic Converter)
Porsche 997S MK2 3.8L (BEFORE Catalytic Converter)

Function:
The Oxygen Sensor (also known as Lambda Sensor) is located in the exhaust manifold and measures the amount of unburned oxygen in your engine's exhaust. Based on the amount of oxygen, it sends a signal to your engine computer which then adjusts the air/fuel mixture for optimum engine performance and emission control.

Failure Symptoms:
Excessive fuel consumption, a faulty oxygen sensor can waste 30% of your fuel.
Driveability problems, such as engine surging or hesitation.
High hydrocarbon emissions, failing an emissions inspection.
The engine warning light may be on or service flag displayed.
The ecu/computer stores a mixture-related fault code.
When the oxygen sensor has stopped functioning completely, the catalytic converter may overheat and fail

Maintenance/Service:
Test and/or replace every 30,000 miles.
Perform periodic emission checks.
Watch for service light.
Vehicle manufacturers recommend periodic inspection and replacement of oxygen sensor.
______________________


I checked the website and the same applies for the 991.

Based on this information and on the report 2 years ago about somebody in UK that solved his stumbling problem by changing the lambda (O2) sensors, I have decided to give it a try.
However, I fear that the oxygen sensors I end up buying are like the ones I might already have: withing spec but so far off from the optimum value that the stumbling problem will persist. So, I wonder:
What brand of oxygen sensor should I buy?
How can I test the sensors I buy to ensure that they are not only withing spec but as close as possible to the optimal value required by Porsche?
I lack the technical knowledge to answer these questions. Your suggestions will be appreciated.

 

Well, this sounds promising at the least. I would say if you are willing, replace the sensors with OEM parts first to prove that changing sensors actually fix the issue. If you replace and the issue is NOT resolved, then at least you can be almost certain that it isn't the sensors that are the root cause. If the problem IS fixed with the OEM sensors, at least you've proven the theory. Yes, they too might fail in the future, however you've got MUCH more position in dealing with the manufacturer if you can point to that root cause (of course they'll want to confirm....).

This being the root cause kinda makes sense:

• The way the issue occurs over time, some sooner than others...
• Not everyone has the issue
• Updating the ECU / software reset seem to temporarily "fix" the problem

Keep us posted. Good Luck!

 

Now we just need a guinea pig or some type of laboratory rodent.

 

I just thought of something..... I might be able to test-out the sensor theory at some level this weekend. I will be attending PCA Tech Tactics at the Easton training facilities - Saturday session. If I can find the right moment, and the right Porsche engineer/mechanic, I'll run this whole issue by them. I mean what better place to bring this up than at a facility solely focused on training P-car mechanics? I'm not talking about the trainees, either. But I'll bet there are some pretty sharp guys running the show over there!

Just too bad my car isn't having this problem! Might have gotten a lift ride out of being there!!

Well, it's just a thought....

 

Plenum:
It would be of great help if a tech could tell you how to test an oxygen sensor to determine its sensitivity and what is the optimal value. Knowing this would help me choose the right sensors before replacing mine.

 

The Oxygen Sensors are actually quite easy to access. Noticed them when I changed my oil last year.

 

I am not mechanical inclined so this info is good to know when negotiating with my tech the price to replace the sensors. Thanks!

 

While the O2 sensors may be promising (and very accessible) I have always suspected the CPS given their history and the fact that the stumble occurs at the exact same rpm.
But any leads are better than none.

 

CPS = Cam Position Sensor?

 

Correct

 

I thought it was crankshaft position sensor.

 

@Plenum - Did you ever get to run this issue by the team at your PCA meet?

Thanks

 

Hi dux- sorry I didn't post anything immediately after the Tech Tactics meet on the 28th. Thanks for reminding me!

The short answer is no - although I had some great technical deep-dive discussions with various engineers (especially around the 918 they had on a lift for us), they were very product specific-or-restoration of older models focused and not able to shed light on the issue (maybe that was on purpose...!). Apparently they didn't have much of the teaching staff around.

Sorry guys.

 

Dang it guys? Still no solution?