Bumping this back up again as now that all of the bad components have been replaced I can accurately report that, although it’s better, nothing I did made the vibration go away. It’s now not speed dependent anymore but there is a strong correlation with RPM with the worst vibrations from about 2500-5000. Doesn’t seem as noticeable at WOT. I didn’t replace the water pump as it was replaced just 5K miles ago by the PO but I did put a new fan in and it still wobbles. Did not replace the uber expensive clutch. Also replaced all of the uber expensive ignition components and had the injectors cleaned and flowed.
Got a dyno pull at Putnam last weekend and the numbers were all over the map. I have no idea how to interpret them or whether to ignore them altogether and try again at a local shop. Since the pulls were asked for by the RD, I only got to look at the sheets, not keep a copy. Numbers were something like 144, 132, 135 RWHP and 132, 121, 125 RWTQ. And spikey as hell.
So what are the potential and likely causes for low(?) output with otherwise good compression over a limited RPM range combined with a nasty midrange vibration? ilateapex suggested:
Throttle position switch
Thermostat sensor
O2 sensor
I think I might add AFM.
Other suggestions? I hate being 6 seconds down. I’d be ready to believe it’s just me and my inability to drive, but I placed 8th out of a field of 40, including GTS3&4 and 944Spec, in the rain. So I get to pretend that it’s the engine.