Yep. Test the ISC, replace if necessary. Make sure coolant isn't getting into the ISC's passages and replace the o-ring between the FIAV and TB.
Since you are going to have the throttle body off (assuming the FIAV o-ring is leaking) you might as well rebuilt the TB now.
I'm not saying to buy your rebuild kit from ebay, just posted the link as an example. The FIAV seal is the funky looking o-ring with 3 passages. This is the seal that is most likely leaking and caused your ISC to shot out, thereby shorting out your ECU
ebay
But I should mention that the ISC may have shorted out and been repaired just no one noticed the damage to the ECU. This is why you should properly diagnose everything before you start throwing parts at the car trying to fix it.
The IC105 controls the ISC. Fixing this may not correct your originial problem regarding fuel consumption and how to tune, or it very well could.
Your original post was about tuning and the use of a logger and SAF-C. If you have larger than stock injectors you can compensate with the SAF-C however it is just a band-aid until you get a better tuning solution. You need to figure out what size injectors are in your car so you can even begin to dial it in.
Now start googleing the crap out of
"How to tune with an SAFC" .