Der Treiber

This is a '90S2, so it doesn't have the wiper arm-style AFM (PPD shows an electronic MAF), isn't that right? I don't know about whether the FPR is to blame since otherwise the engine runs smoothly, and other symptoms usually blamed on an FPR don't seem to apply. Vacuum lines, I guess. They generally look and feel in good shape, yet. This S2 only has 66k on it, so it's not like they're full of carbon gunk. Would they cause a slight stumble at a specific RPM, just because they're older? If not, does that get us back to the ref sensors...you know, now that I think about it, the connector on the cam sensor wiring harness is busted up, and taped up w/ electrical tape...maybe there's a cam frequency at which that connector is just bugging out a bit.

konakat

Testing vacuum is pretty easy with an air compressor and a couple dollars worth of fittings from the hardware store. Here's the procedure: http://forums.pelicanparts.com/porsc...oooo-easy.html

Also, isn't all that fluff on the engine side of the air filter? If so, you may have some fluff stuck somewhere.