Bad O2 sensor cause misfire?

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I would bet you $100 that it is not the plugs. I would bet you the same amount that three coils did not go out at the same moment either. And your MAF is not going to cause a misfire and if it could (but it can't) why on only one bank and not the other.

Like I said these are all symptoms. What chain of events could cause them all to happen? What are the things that tell the ignition system when to fire? Crank position sensor? Cam position sensor? This is where you start.

Have a good Porsche mechanic look it over for you.