True but ISTR on all of these systems fuel enrichment when you push the throttle is determined by how much air is drawn in, be it measured by a AFM or a MAF. The question is how does the car drive at constant throttle?
TBH the 3 cases I know of when the FPR has required replacement (2 for me and a friend) the result was to high fuel pressure which made the car run rich and rough feeling, but otherwise drive OKish.
My 968 was/is suffering from a misfire due to running very rich but this only happens if sat idling for a long time and this is on a car where the emissions are going up to 7% and HC up around 1000 ppm sometimes. The ignition is amazingly strong in these cars (when fresh), it seems to be able to burn even when running amazingly rich.
So I agree with the previous posters as a first port of call, unfortunately checking fuel pressure and leak down for most is a Porsche specialist job. Fuel filter should always be replaced if one doesn't know how old it is and should be replaced every 24K miles or so anyway, also the bottom of the tank could in rare cases get blocked up with crud and little stones. If the fuel supply is ok then AFM / TPS checks up around that area would be next port of call for me. Basic fuel supply can be checked with the supply disconnected a measuring jug and a stop watch, but TBH I have only done that once many years ago and it told me the supply rate was within spec [wasn't on a 944 btw].
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