Quote:
Originally Posted by autojack
One other thing to mention: my speedometer has been intermittent since I got the car, and it was not working when I drove to the test place. But they didn't comment on it, and it worked on the drive home. Does the speed sensor feed the DME at all?
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Can't answer if the DME and its control is affected by vehicle speed.
If your car does have EGR, its sole purpose is to control NOx so it would need to be inspected for proper function.
Your NOx is elevated but not of the charts. Your only off by about 100 ppm on the 15 mph and right on the line at 25 mph. So if you have no EGR, you
might reduce the NOx some by adding a higher octane fuel. Also, as mentioned, your CAT may be getting weak so the slightly rich mixture may be affecting its efficiency enough to put your NOx over the edge. Not sure if your car was warmed up enough before the test was done but a hot CAT works best. Another possibility, could be carbon build-up in the cylinders causing higher cylinder temps and raising the NOx. I am more experienced with non-Porsche engines so perhaps someone else can comment on whether carbon build-up is an issue with these engines. My guess is no since most of us are usually in the "Italian Tune-Up" mode of driving
So, since you are close to passing and assuming there could some carbon build-up, a low-cost DIY attempt to reduce your NOx could be to add some premium fuel and run some Sea Foam induction cleaner through a vacuum line to clean any intake deposits and carbon. I have had good luck with these remedies on smog/Nox failures that like yours that are close.
Most of my experience is with non-Posche engines so If Sea Foam or similar intake cleaner is not recommended someone please advise.