[Porsche-O-Phile]

The good news is it sounds like nothing mechanical - so a lot of really tedious & expensive repairs are out as a cause.

This leaves the basics - air, fuel, and spark.

Is it possible that you have an intermittant air supply blockage? Unlikely.

Fuel - it sounds like possibly an intermittant fuel starvation problem could cause this - check for pinched lines, clogged lines, bad filter, bad fuel pump, etc.

Spark - could be loose coil wire, or possibly the computer control (DME) or its relay, like AFJ said. Start with those things and take it from there.