I have an 05 997 57k miles, with the misfire code issues. New plugs, new coils, just had the ECU re-flashed.
The car runs great.

Has anyone found a solution?

 

I just had a flash done, and can't get rid of my CEL. In my case, I'm 99% sure it's the tune. I'm still going back and forth with the vendor, VR Tuned. They send me a revised file, but it only worked for about 50 miles. My car has also been running great. Your issue could easily be flash-related as well. Who did your tune?

 

Just had the dealer re flash with the latest Porsche software.

 

Diagnosing persistent misfires after addressing the most likely causes -- plugs/coils -- is a real pain.

Persistent but random misfires over a number of cylinders on both banks. This suggests a common failure mode.

One cause can be a bad MAF. But it can be a bad wiring harness or a bad DME.

As an aside, "bad wiring harness" can be bad due to rodent damage.

Misfires confined to more than one cylinder of a bank. Again a MAF can be at the root of this. For some reason one bank is more sensitive to the effects the bad MAF causes.

But a bad wiring harness or bad DME again have to be considered.

Another explanation can be a problem with the VarioCam Plus system. The low to high lift switching mechanism (a high pressure oil "circuit") is bad. Fortunately the portion of this circuit that most often goes bad is in the lifter so the solution is to replace all intake lifters of the misfiring bank.

A persistent misfire of just one cylinder can be a bad intake lifter in which case this can be addressed by replacing the intake lifters of that cylinder, though I believe Porsche -- at least for cars under warranty -- would just have all intake lifters of that bank replaced.

The misfire can be caused by a bad coil/wiring harness connection or a bad wiring harness or even a bad DME.

Another source of a persistent misfire confined to one cylinder is a burned exhaust valve.

A compromised piston/ring/cylinder seal can also be at the root cause of a misfire.

In the case of a suspected burned exhaust valve or a compromised piston/ring/cylinder seal a compression test and leak down test can help. The compression test will help one to know there is a mechanical explanation for the misfire by finding one or more cylinders low on compression and the leak down test will help one identify what is the problem with compression.

if a compression test finds no compression problem then the misfire is probably due to a wiring or DME problem.

However, a road test might be necessary to eliminate the low to high lift system.

Remember, a misfire is an underperforming cylinder. For some reason the cylinder isn't receiving a proper intake charge -- intake valve lift problem -- or does not combust this properly -- bad plug or coil -- or can't contain the combustion created pressure -- bad exhaust valve or bad compression -- and the DME detects this by the particular cylinder's lack of contribution to the flywheel's speed and flags a misfire code.

The factory manual has a very large section concerning misfires and the possible causes and the steps or tests to identify the cause.

Either you have to be prepared to do the diagnostics or have them done by a qualified tech.

 

If its the multiple cylinder mis-fire(s) that gets thrown during cold start idle, try replacing air filter with stock and clean the throttle body... Just google "997 Throttle Body Cleaning"