Cool .. I knew you would
... I've had 2 of these fail on different cars over the last year so I'd think there would be a good chance that the sensor will be the cause of the fan run on ... the rough running will be probably be less easy to track down but most of the things that you do on the hunt will be beneficial for the future good running of the car so not lost time or $$.
I had a 944S that I had that I checked everything on only to find a new set of plugs did the trick
... for the S2 go for Bosch OEM copper WR5 DC+ ... I've not had good results with platinum/iridium etc. Cockerpunk maybe right ... plugs, leads, cap and rotor are an easy swap out and worthwhile if running original Beru set up, but I'm not sure if I agree with him re 'cheap' - these parts are pricey for the 16V cars. Don't go for chinese leads. Stick with Beru/Bosch caps ... I found some Bosch leads with Beru caps that were cheaper than Beru/Beru and good quality. Have a good hunt on Ebay or Pelican do a reasonable value 'Tune up kit' too. Have a really good look at any service records that came witht he car. If something has been changed in the last few years then you obviously don't need to be changing it again.
All these little things tend to be ignored by 'previous owners' and you will be plagued with niggley problems until you go through and check/replace the items discussed above. the cars are 23+ years old and a lot of the sensors and rubber suspension components are passed their usable life - they may still be functioning but at any moment .... they won't